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Vortex aerator vs airstones

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Anybody have any thoughts on using a vortex aerator for the fish tank rather than air stones? To clarify: what I mean by 'vortex aerator' is simply a bucket with a hole in the bottom suspended over the fish tank, and a small submersible pump hanging underneath it just below the surface of the water which pumps the FT water into the bucket at a tangent. This creates a swirl in the bucket as it drains back to the FT which supposedly aerates the water very well. Since I haven't seen any decent sized air stone kit where I live (Ecuador) and would probably have to have it shipped in, a small water pump and bucket would be a lot easier to get hold of.

 

BTW, I'm new, so hello everyone.

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Hi Mark,

Welcome abooard.

There are many ways to introduce aerate fish tanks other than airstones......including cascade aeration.  You can also use so-called "powerheads" - pumps used in reef tanks to simulate wave action......and you can mount a small submersible on the bottom of the tank with the discharge located far enough below the surface that it just causes an 'upwelling' action.....causing the water surface to change frequently.  The point at which the water suface meets with the air is where most aeration occurs.

Gary

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Thanks Gary, phri, all great suggestions. I guess the follow up question is which of all these varying methods is more efficient, in terms of energy use, ease of set up, and results. Anyone have any idea?

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Hi Mark, 

First welcome to the forum.

Second, I'm curious if the issue is acquiring  an air stone or air pump.  A airlift pump which is basically a vertical tube in a pipe with an air line at the bottom ( no stone needed) is vastly more efficient in terms of  energy and ease of use. This does depend on depth of the fish tank though.   It also depends on the size of the tank as well.

I've used the spray bar attachment Phri suggested in the past.  I simply oversized my main pump and bypassed some of the excess flow through the bar, plus the return from the growing system broke the water surface and provided some aeration.   A little detail on depth of tank and size of system would be helpful in figuring out which are better options for your setup.

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Hi Ravni - thanks for the welcome! There is an issue with acquiring an air stone/pump - I live in Ecuador and I've never seen any here other than tiny little aquarium models. I can always order them from Amazon and pay the rather high import duties we have here, but I'd rather use something that's readily available locally. Right now I'm tinkering with plans for an iAVs system, and the choices are between having one sump pumping to above ground tanks which drain via a SLO to the GBs and then back to the sump, or below-ground tanks as in the classic iAVs system with no sump, the water pumped out of the FTs to the GBs, and then draining back to the FTs. In either case the FTs will be around 2,000l and about 1.5m deep. Four tanks so I can raise the fish in cohorts and get a fairly consistent nutrient supply to the GBs. If I remember right, Mark McMurty found the best ratio of FT volume to GB volume to be 1:2.2, so that would give me 15 grow beds of 1mx2m at 30cm deep. Since I think it's probably better to have the FTs aerated 24/7, even with tilapia (I could be wrong), and the iAVs system only has intermittent pumping, I need some sort of separate set up for the aeration. When I was originally thinking about a continuous flow system, I was just going to include a trickle tower, but with iAVs that's not really an option, I don't think. Weren't you experimenting with iAVs?

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I experimented with adding a sand bed to my existing setup.  Unfortunately, I lacked some understanding and made several errors with that trial, but still got what I felt were good results with it.  I needed a better drain system and my sand choice had more small particles than recommended which led to having to further altering fill times to keep from overfilling.  So don't go cheap on a timer or select inferior sand if doing IAVS.  That  said even my poor replication produced significantly better than my continuous flow systems with the more "classical" approach to AP.  

Tilapia can handle poor water better than most other fish, but if you are willing to run a second water pump you can do the spray bar with one and sand beds with the other.  Another option is to use a venturi to suck in air into the exhaust side of your pump and mix air and water.  Aquariums use  that sometimes as well.  If your stocking density is light enough you won't have to have additional aeration but the drain from time to time, so that is another consideration.  A key factor sometimes overlooked is the greatest time oxygen is used up is when feeding, so feeding is not done after 1 pm or so , so that then next few cycles compensate for that and then its in idle until morning.

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Thanks for the input Ravnis. I'm trying to get my head around the cost-benefit of all these variables. Will the cost of running aeration 24/7 outweigh the benefit of presumably faster-growing healthier fish? Or will the benefit of being able to stock more fish via 24/7 aeration and therefore having more crop growing area outweigh the cost of the aeration? How much better do tilapia do with 24/7 aeration? Enough to make it worthwhile? This is important to me because where I am (up in the Andes) it's much more difficult/costly to get the conditions right for the fish than it is for the crops, so maximizing the fish efficiency is a biggie - the more fish I can have in the same-size (insulated) fish tank area, the more crops I can grow. I know I'm probably just going to have to experiment myself to get these answers, but if you can shine any light on any of this you would be doing me a big favor! I don't expect to get up to anything like the stocking levels of pure RAS, and nor do I want to - way too much technology involved - but I'm definitely leaning towards more fish is better than less.

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Oh, up in the mountains....   that complicates matters some.    I will caution you this.  Heating water for fish in an uninsulated greenhouse will empty your pockets and produce fish that cost up to  $500 dollars a pound.  I wish I could say that was not from experience, but it is.    Also at higher elevations , you will have more difficulty getting oxygenation levels in your water, so oxygenation methods need to be really thought out.   

Is there a local fish to your liking and climate that you might consider growing? From my experience, mossambique tilapia can be adapted to survive around 44 to 46F temps for short times, but this took me three years to get them acclimated.  There are probably other methods as I am no expert, but an amateur at fish keeping and raising.  They will not grow and weaker ones will die at that temperature. You need 76F  or warmer water for good growth. 

Are you going to use a walapini type greenhouse ?  Is solar water heating an option for you?

Edited by Ravnis
correct insulated to uninsulated (see edit history)

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The greenhouse is already pretty much built, just a few finishing touches needed. It has insulated polycarbonate walls and roof, insulation on the ground to prevent heat loss that way, and I'm going to put about a foot of sand/gravel on the floor for thermal mass. Remember we're up in the mountains, but also on the equator, so the temperature inside this GH gets up to well over 100F during the day. I'm hoping with all the thermal mass and insulation the temps won't drop too much at night. That remains to be seen. The crops greenhouse will be way cooler during the day, suitable for tomatoes, but I'll be running the water back to the fish house via black irrigation pipe. Since the water will only be exiting the fish house during the day, I figure I can just add more and more black pipe between the grow house and the fish house until the sun-heated water is coming back to the fish at the right temp. In terms of fish species, fingerlings are only readily available for two species here, tilapia and trout, and from what I've heard and read trout are way more trouble to raise. That's the theory anyway! The effect of altitude on oxygenation is a really good point, and it leans me even further towards 24/7 oxygenation. Maybe a small pump for each tank going up to a trickle tower using lava rock? Would that give more DO than a spray pipe? Here's some pics of the GH.WP_20160717_007.jpgWP_20160717_005.jpgWP_20160717_004.jpg

The insulation is polystyrene tiles, some sort of packing material which I picked up from my local recycling place.

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Before you fill the greenhouse with sand/gravel , take a look at sunny john subterranean heating and cooling. You may want to seriously consider adapting that for your greenhouse.

I'm not sure which method is more effective. One issue I do know is the continuous  pumping to a spray bar or trickle tower will break up waste products and produce suspended solids and I've been trying to think of a solution that does not do that myself and the light bulb has not come on yet.

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8 hours ago, Ravnis said:

take a look at sunny john subterranean heating and cooling

This is a really nice idea - the Sunny John website doesn't seem to exist any more, but the whole heat sink idea is out there and seems simple enough, especially since I already have most of the work done for installing the pipework. According to the YMCA at Virginia Tech (makes me think of Roxy Music, shows my age) project, the amount it cools/heats does not seem that great, but I'll take the day/night temps in the GH this weekend and see how much I actually need. I also need to stick a tank of water in there and see how much the water temps vary day and night, which is the important thing since I'll probably only have fish in this GH.

 

8 hours ago, Ravnis said:

One issue I do know is the continuous  pumping to a spray bar or trickle tower will break up waste products and produce suspended solids

A very good point which I hadn't thought of. One of Gary's suggestions was a pump up-welling water from just below the surface, which wouldn't break up larger detritus since there's no splashing, but I don't know how effective it would be at oxygenating.

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Some observations I found from overwintering.

Having a fan pointed at the fish tank cooled the air and heated the water with minimal additional energy.  Worked best if on during daylight and off at night.

a 16 ft x 4 ft solar water heater made from pex pipe and radiant floor fins with a 300 gph pump would give my ~5000 gallons an 8 degree rise over the coarse of a sunny day with outside temps  20F. 

On sunny days even with temps in the 20's F the greenhouse temp would reach high 80's to 90s.  This was with just film covering.  Long streaks of cloudy days would require supplemental heat.  A plan for that in the building stage would be much easier than trying to rework it when it's filled.  You may not have low enough temps to need to worry it.  As a very loose rule of thumb, an average of highest temp and lowest temp would be close to the water temp without any additional heating.

Hope I'm not sounding to critical, I just want to see you avoid some of my mistakes if you can.   It may be a trick of light , but it looks like there is a bow in your roof that could catch water/snow.  Weight of this can get heavy if it cannot drain fast enough during a storm and crash in your roof.  Might want to verify that won't be an issue. 

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Guilty as charged - there is indeed a slight bow in the roof. Basically I would either need more rigid roof beams or central supports to fix it. However, we never ever get snow here, and the rain runs off no problem, so I'm just leaving it as is. Next time I'll know better! I feel for you if your daytime temps get down to 20F! Here, it almost never gets down to freezing. Usually the lowest nighttime temperature will be around 40F. Remember, we're on the equator, so we basically have two seasons: slightly cooler and rainy, or slightly hotter and windy. Think permanent spring. Even at some 9,500ft above sea level, daytime temperatures right now are in the mid-70s and nighttime in the mid-40s. 

2 hours ago, Ravnis said:

Long streaks of cloudy days would require supplemental heat.  A plan for that in the building stage would be much easier than trying to rework it when it's filled.  You may not have low enough temps to need to worry it.

I'm going to measure all the temps this weekend. If the nighttime temps are low enough to warrant it then I'll definitely consider the heat sink and install that before putting the gravel and sand in. Actually, I'm now thinking of bricks - more stable and apparently better at absorbing the daytime heat, at least if they're denser than sand, which I think they are. Thanks for the great tip!

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If 40F is as low as you get I don't think you have anything to worry about as far as temps.  Especially if its like my early fall where it's only 40f for a couple of hours in the morning and actually much warmer.  If thats the case I would expect  water temps with a greenhouse setup to be high 60's to low 70s.

 I like the brick floor idea though.  I'm currently having issues with weeds growing through the sand/gravel floor.  It will also make it easier to level. Sand is also a horrible heat sink material as compared to water or rock.  It tends to insulate.

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Definitely more like your early fall, except with the temp inside the greenhouse getting to well over 100F during the day. If I can keep the GH temp falling too much at night by using passive heating, then I think I should be ok for the tilapia without too much effort - ideal water temp around 80F.

Right now I have plastic on the ground, then nearly a foot of recycled polystyrene tiles on top of that, which I think is probably way too much, but I can always take some out and use them for something else. I don't think many weeds are going to grow through that, but they can definitely seed in sand, so I think I will probably just lay bricks down on top of the insulation. I was just reading that the sun will only warm around four inches into a heat sink during the day, so I'm going to just lay one layer of brick and see what nighttime temps I get with that. If it's not enough, then I can do the whole pipe and blower thing and lay another couple of layers of brick, the top layer to be heated by the sun and the lower two by the hot-air pipe. Brick is definitely going to make leveling easier.

Any thoughts about the up-welling water for oxygenation without breaking apart the poo idea? Have you tried that?

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Oh tried various methods over the years.  My only guide has been whether the tilapia stayed at the water surface that indicates low oxygen in the water as I didn't have a oxygen meter.    The spray bar did well, and the trickle tower did well.   I did have a time when the pump got disconnected from the exhaust pipe and it sat upwelling instead of pumping to growbeds.  The fish did not gulp then either.  Phri is a professional on this board, so he may have some actual numbers as to which may be the better solution for you.  He may need more information, though.

 I wound up growing fish with a little used option of greenwater , but it required a very good air pump, so I invested in a medo air pump with rubber membrane air stone and never looked back. It was not cheap, but after buying the cheaper air pumps  over and over again after they wear out it wasn't that much more expensive in the long run.

As far as the altitude... take a look at this graph,  if your not that high up it may not be anymore an issue than temperature for you.  

altitude oxygen chart

As you can see the oxygen starts dropping slowly at first, but accerates faster as elevation increases.  Up to 2000 feet the drop is minor as compared to 6000 feet.

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Just a thought, maybe just run the "oxygenation pump" on a timer after the timed cycles to the growbed are done and run until first feeding. If the solids have been cleared to the beds, should not have to worry about the "oxygenation pump" making suspended solids.

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11 minutes ago, Ravnis said:

My only guide has been whether the tilapia stayed at the water surface that indicates low oxygen in the water as I didn't have a oxygen meter.

I think I'm going to have to bite the bullet and fork out $200 or whatever it is for a DO meter, because according to that chart we're at the same level as Aspen with around 30% less oxygen than sea level, so DO could well be an issue. With the meter I can just try out the various methods for oxygenating while not breaking up the solids and see which works best. Or I could just PM Phri and see what he says!

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4 hours ago, Ravnis said:

Just a thought, maybe just run the "oxygenation pump" on a timer after the timed cycles to the growbed are done and run until first feeding. If the solids have been cleared to the beds, should not have to worry about the "oxygenation pump" making suspended solids.

At your proposed stocking density....and the ratio of fish tank to growbed volume.....you are not likely to experience water quality issues.....particularly if you don't feed later in the day.   From the last irrigation cycle in the evening - to the first one the next morning - you are not likely to have much in the way of solids in your system that a water pump could macerate.

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8 hours ago, GaryD said:

At your proposed stocking density....and the ratio of fish tank to growbed volume.....you are not likely to experience water quality issues.....particularly if you don't feed later in the day.   From the last irrigation cycle in the evening - to the first one the next morning - you are not likely to have much in the way of solids in your system that a water pump could macerate.

Using Mark McMurtry's model, the stocking would be 80 fish per 1,000l (250 gallons) and a volume ratio of 1:2.2. Harvesting at 500g (1lb), that would give me a density at harvest size of 40kg (80lbs) per cubic meter of water (250 gallons), which seems quite high without all the bells and whistles of pure RAS - Wilson Lennard for example recommends a density of no more than about 17kg per cubic meter of water, although to be sure that is for the less efficient filtering of gravel grow-beds. In addition there is the problem of reduced oxygen at altitude - and according to the chart Ravnis kindly pointed me to, I have around 30% less available oxygen here than at sea level. So, the question is, can I safely rely on just the oxygenation from the water intermittently falling into the fish tanks for 15 minutes or half an hour every two hours during the day, given that I only have 70% of the oxygen available in the air that I would have at sea level? If I can, and if I only feed the fish twice a day, say at 10am and 12am, so the solids have time to settle and get pulled out by the last few drains to the grow beds, then, as you say, I can just run a separate aeration system during the night and not have to worry about suspended solids. My concern, though, is that intermittent cascade aeration won't be enough during the day with my reduced oxygen levels, along with the fact that research seems to indicate that it's better for fish growth to feed smaller amounts more often than larger amounts more infrequently. The feed manufacturers also recommend this. I know the focus is the plants, but I'd like to also farm the fish as efficiently as I can within those parameters. So, those are the questions I'm pondering right now. I see a very expensive DO meter and a lot of trial and error in my future.

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Found a study on fish grown at varying oxygen levels.

effect on oxygen and fish growth of halibut

found  a comparison of aeration methods with some formula's.  Most of the formula's  I struggle with (haven't done that kind of math since the 70s), but might give an idea or two.

aeration comparison

Found it interesting that altering certain variables  increase stripping of gas, and other increased absorption.

 

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Thanks for this Ravnis! The study on DO and fish growth really hit home. Who wouldn't want to take an extra bit of trouble and spend an extra bit of money on oxygenating if it's going to DOUBLE fish growth? And reduce or even preferably avoid disease. I knew DO was important, but this really shows how important. Even if we're focusing on crop rather than fish production, faster fish growth means more poo, and more poo means more crops. To quote the study (which is quoting another study):

"An experiment done on tilapia (Oreochromis niloticus) showed that FCR was inversely proportional to the dissolved oxygen level (1.45 at higher dissolved oxygen level and 6.75 at lower dissolved oxygen level) (Tsadik and Kutty 1987)."

That's a HUGE difference. I'm amazed.

 

According to the other study, one huge waterfall is very good at increasing DO, but having the water fall down lots of little steps instead of one big one actually encourages DEgassing. Interesting. I suppose the bigger the splash, the more contact with the air, hence more absorption - but why small splashes would encourage the opposite, I don't know. Also I'm not sure from the study if he's referring to just oxygen, since it's about getting nasty things like CO2 out of the water.

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Mark your greenhouse looks pretty good.

I am a bit skeptic about the statement of a fcr inversely proportional to DO (sounds more like a lab-fart to me).

If DO is sub-optimal fish will simple reduce feed uptake as oxygen requirements are directly related to metabolic rate for digestion/growth (we ignore basal/fasting metabolic rate here as its relatively small). In my book reduced growth due to reduced oxygen availability isn't necessary going to result in huge differences in feed conversion ratios, and definitely is not going to give this inversely proportional relation.

As for feeding frequency during 24 hours. Fish grow when nutrients are available for growth, there are no large reserves for protein/amino acids in it's body, which means that after a meal is digested the limited availability of building blocks for new tissue can result in reduced growth. This means it's time for the next meal.

Lenght (time wise) of availability of nutrients after food intake depends on digestion speed which is related to digestibility of food, metabolic rate and meal size (and a couple more variables). Just remember that optimal feeding frequency is related to individual weight; small fish need to eat often (maybe 6 X a day) while lager fish still can have maximum growth while fed 1 X a day.   

As far as I know fish need a minimum DO (mg/l) to be able to absorb sufficient oxygen to sustain max growth. This level is species and conditions specific. Around 5 mg/l oxygen should be ok in your situation, while saturation levels are around 6 mg/l in your conditions; meaning you need minimum 80% oxygen saturation all the time.

Growing warm water fish at altitude is going to be challenging especially with limited resources. I agree with Gerry I don't see any issues here with solids. btw tilapia can handle very high levels of suspended solids without problems; for example they keep them in biofloc systems with great success.

Mark to work out your aeration needs is a bit tricky with the info we have here; things like temperature & oxygen demand of the water can have a large impact on this. Aeration with airstones seems to be the easiest way to solve this. You mentioned that you don't have access to good local airstones, how about leaky hose as used for irrigation? If you don't have this pvc pipe with rows of 1 mm holes can create decent air curtains in fish tanks. You can do this as follows; choose the number of holes so that the total hole area correspond with the total area of the outlet of the airpump. Example airpump has a 12 mm outlet is approx.  144 holes of 1 mm.  Choose an airpump/blower which has enough grunt to delivery sufficient air at the lowest point of your tank. As a guess you are going to need an airpump which can move at least 2500 m3 air/hour at the depth of the manifold per m3 of fish tank. This is high because of the averse conditions and planned high stocking rates.

40 kg fish/m3 is high, while doable for a pro I wouldn't go that high, can't you just increase fishtank volume to reach the same level of fish output with lower densities?

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