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markor58

Vortex aerator vs airstones

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10 hours ago, phri said:

Mark your greenhouse looks pretty good.

Thank you! It cost enough (mainly for the polycarbonate). I finally got around to measuring the temperatures in it this weekend - even with two end sections and all the little vent windows at the top completely open, daytime high was 40C (104F) and nighttime low (it was a chilly night for Cayambe) was 6C (43F). According to Ravnis the fish tank temps will be roughly halfway between these two extremes, meaning that just by adding a brick or concrete slab floor as a heat sink to provide a bit more warmth at night I should be able to get ideal temps in the tanks, I hope.

10 hours ago, phri said:

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.

I think it just boils down to it's better to give them more DO than less. I've now seen that there are chemical DO tests you can get which are far cheaper than the digital meters, which you still have to change membranes etc. on once a year, so I think I'll get some of those to make sure the DO is at the right levels. Regarding DO, I agree the simplest method seems to be airstones. I'll just get them from Amazon - you have to pay a $45 tax on small stuff shipped in to Ecuador, plus the shipping, but what the hell. I think I'm going to get the Elemental O2 Commercial Pump, 1744GPH, which costs around $70, and see how many tanks that will aerate to good levels. I tried a simple experiment with the centrifugal blowers which are widely available here, since I had one lying around, and quite apart from the problems attached to them being low-pressure devices, I'd forgotten how noisy they are!

10 hours ago, phri said:

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?

I agree it seems high - I just pulled that figure from Mark McMurtry's experiments back in the 80s, where he used 80 fish per 1m3 tank. Wilson Lennard recommends no more than 17kg/m3, which would be 34 fish at harvest weight of 500g, or maybe 50 if I harvest at 350g. Apparently the cost/benefit of feed input versus growth rate isn't worth it past 350g, after which tilapia growth slows considerably - do you have any thoughts on that? Best harvest weight? Anyway, I think I'll start with 50 fish per m3, and see how it goes as they grow.

Thank you for your valuable insights, Phri, I really appreciate it.

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1 hour ago, markor58 said:

Thank you! It cost enough (mainly for the polycarbonate). I finally got around to measuring the temperatures in it this weekend - even with two end sections and all the little vent windows at the top completely open, daytime high was 40C (104F) and nighttime low (it was a chilly night for Cayambe) was 6C (43F). According to Ravnis the fish tank temps will be roughly halfway between these two extremes, meaning that just by adding a brick or concrete slab floor as a heat sink to provide a bit more warmth at night I should be able to get ideal temps in the tanks, I hope.

The best heat sink is probably water. I am not sure about the temperature being in the middle of day and night. Night losses are probably mainly convection while day heat gains are through radiation. These don't have to be equal (I would expect a higher then the average temperature).

I think it just boils down to it's better to give them more DO than less. I've now seen that there are chemical DO tests you can get which are far cheaper than the digital meters, which you still have to change membranes etc. on once a year, so I think I'll get some of those to make sure the DO is at the right levels. Regarding DO, I agree the simplest method seems to be airstones. I'll just get them from Amazon - you have to pay a $45 tax on small stuff shipped in to Ecuador, plus the shipping, but what the hell. I think I'm going to get the Elemental O2 Commercial Pump, 1744GPH, which costs around $70, and see how many tanks that will aerate to good levels. I tried a simple experiment with the centrifugal blowers which are widely available here, since I had one lying around, and quite apart from the problems attached to them being low-pressure devices, I'd forgotten how noisy they are!

Don't get me wrong here I don't recommend to run below optimal levels of DO, but just find the relation between DO and FCR unlikely. The pump you intend to buy isn't too bad, but don't expect it to be low noise!!! A low noise good unit is  http://www.ebay.com.au/itm/like/271956103161?lpid=107&chn=ps I have one of the big one here running but not from the same seller.

I agree it seems high - I just pulled that figure from Mark McMurtry's experiments back in the 80s, where he used 80 fish per 1m3 tank. Wilson Lennard recommends no more than 17kg/m3, which would be 34 fish at harvest weight of 500g, or maybe 50 if I harvest at 350g. Apparently the cost/benefit of feed input versus growth rate isn't worth it past 350g, after which tilapia growth slows considerably - do you have any thoughts on that? Best harvest weight? Anyway, I think I'll start with 50 fish per m3, and see how it goes as they grow.

I would advice to not start to ambitious and gradually increase stocking in line with your experience.

All fish slows down in growth when size increases, but growth when they are bigger comes at a relatively lower cost with regards to inputs (other then food). You have to do a full cost-benefit analysis too work this out and look at market value of the different sale sizes.

Thank you for your valuable insights, Phri, I really appreciate it.

No worries....I am slowly turning into an Aussie.........

 

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8 minutes ago, phri said:

The best heat sink is probably water. I am not sure about the temperature being in the middle of day and night. Night losses are probably mainly convection while day heat gains are through radiation. These don't have to be equal (I would expect a higher then the average temperature).

I think we're into suck-it-and-see territory here. I already have the insulation down (way too much probably, but there you go), and I need to put a solid slab floor on top of that anyway, so once that's done I'll put in a first tank and just see what water temps I get. I'm hoping I won't need more ventilation than a mesh-covered opening at ground level and just leaving the upper vent windows open as they already are, covering them with mesh to keep the bugs out rather than more polycarbonate. Only time will tell.

15 minutes ago, phri said:

Don't get me wrong here I don't recommend to run below optimal levels of DO, but just find the relation between DO and FCR unlikely. The pump you intend to buy isn't too bad, but don't expect it to be low noise!!! A low noise good unit is  http://www.ebay.com.au/itm/like/271956103161?lpid=107&chn=ps I have one of the big one here running but not from the same seller.

Thanks for the link - that thing looks a beast - I counted 32 outlets on the manifold. It says 'Resun' on the label of the compressor shown in the picture, but the page title says it's an Elemental O2 model. Are they the same manufacturer? Anyway, looks a great buy.

17 minutes ago, phri said:

I would advice to not start to ambitious and gradually increase stocking in line with your experience.

Absolutely - I have a tendency to fly off into dream land, but thankfully I also have a wife who brings me sharply back to earth!

18 minutes ago, phri said:

All fish slows down in growth when size increases, but growth when they are bigger comes at a relatively lower cost with regards to inputs (other then food). You have to do a full cost-benefit analysis too work this out and look at market value of the different sale sizes.

Yep - the fillets sold in the biggest supermarket chain here seem to come from 350g-size fish, and sell for around $6 a kilo - but if you go to a local street market they sell 1kg-size whole tilapia for $4. Basically I'll only know which route gives me better net returns when I get to that stage. I know you're supposed to have the whole marketing side sorted before you even start, but it isn't that easy here - different culture, etc.

25 minutes ago, phri said:

No worries....I am slowly turning into an Aussie...

I'm English, but I like saying 'no worries' too! I also love all the Aussie slang connected to drunkenness - technicolor yawn, worshiping at the porcelain altar - love that stuff! How can an Australian be insulting when they call you a 'Pommie drongo.'? It just makes me smile.

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On July 22, 2016 at 5:49 AM, markor58 said:

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 -

1. I've never claimed growing out to 500 g at this density

2. I started culling ('thinning the herd' ) at Pmf +/- 250 g. (I have no idea what a target 'maximum' would be, did not attempt to determine that)

3. at v:v 1:2 and N = 80 m-3 : 80 @ 250 g = 20 kg m-3  (120 days per cohort = 60 kg m-3 yr-1)

4. at v:v 1:3 and N-120: 120 @ 250 g = 30 kg m-3 yr-1 (120 days per cohort = 90 kg m-3 yr-1

NOTE: chances are good that posting of this response will be delayed by several days if recent trend continues - not my fault/problem

 

 

Edited by Mark McMurtry
typo (see edit history)

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11 minutes ago, Mark McMurtry said:

1. I've never claimed growing out to 500 g at this density

2. I started culling ('thinning the herd' ) at Pmf +/- 250 g.

My apologies, Mark - a case of 'assume makes an ass...' etc. Your clarification definitely - um, clarifies things. It also confirms (thank you) that I should be about right starting with 50 fish per m3, which will give me a biomass of 17.5kg/m3 at a harvest weight of 350g, 25kg at 500g. If that ends up being too high I can always start culling as you did and then reduce the density for the next cohort. Usually they sell tilapia fingerlings by the thousand here, but I'm sure I can find someone to sell me just a hundred.

24 minutes ago, Mark McMurtry said:

NOTE: chances are good that posting of this response will be delayed by several days if recent trend continues - not my fault/problem

I think your posts are being vetted!

BTW, thank you for the layout drawings - I know you can't eat appreciation, but I appreciate the time you must have put into it nonetheless.

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Hi Mark,

Couple of remarks:

Might be a good idea to have some nursery tanks (smaller).

Don't focus to much on a fixed density (like 17.5 kg/m3) as conditions might not represent your situation and thus loose validity.

As for the resun air pump, is the same, and on the market under a range of names; is about marketing not the product.

It is going to be hard to compete with $ 4 /kg for a small production unit (if that's your plan).

Best to see this as a pilot not as a commercial unit jet.

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Hi Phri

48 minutes ago, phri said:

Might be a good idea to have some nursery tanks (smaller)

Is this in case I want to breed my own? I might be doing that at some point, but right now with tilapia fingerlings selling for $55-$80 per thousand here, I'm thinking it's probably more efficient to just buy them, so long as they're good stock. There's a local-government-funded tilapia farm not too far from us where they do research and outreach and also sell fingerlings, so I'll be getting the fingerlings from them to start.

53 minutes ago, phri said:

Don't focus to much on a fixed density (like 17.5 kg/m3) as conditions might not represent your situation and thus loose validity.

Yes, I think I'm going to stock 50 fingerlings/m3, keep monitoring the water conditions, and cull them if conditions decline as they grow until I find the best density for my situation.

 

55 minutes ago, phri said:

As for the resun air pump, is the same, and on the market under a range of names; is about marketing not the product.

Ok, I think I'll just get that make then - apparently if you hang them off a bungee cord they make less noise!

 

57 minutes ago, phri said:

It is going to be hard to compete with $ 4 /kg for a small production unit (if that's your plan).

My plan is to sell the fish for enough to cover the cost of feeding them, and maybe cover the electricity for the pumps/aeration as well if I'm lucky. Tilapia feed here sells for around $2/kg for the small fish and around $1/kg for the adults, and electricity is pretty cheap, so I don't think it'll be too hard to at least break even. The profits will supposedly come from whatever veg/fruit I grow in the system - right now I'm thinking tomatoes, tomatillo (possibly used to make our own salsa verde), or maybe uvilla, which you might know as Cape gooseberry.

 

1 hour ago, phri said:

Best to see this as a pilot not as a commercial unit jet.

Absolutely! I'm going to start with either a 2m3 or 4m3 fish tank and grow the fish through from fingerlings to harvest in that, so I can work out best stocking density, best filtration area, and so on. Also whether it's worth doing at all! So for the time being I'm going to have rather a large greenhouse for rather a small tank - but if it doesn't work out I can always turn the GH into a very big sauna!

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my observation on the Sunny John system is that it cools better than heats. an other site to look at is 'oranges in the snow' I am at 5600 f

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