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Some questions for experienced AP'ers.

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Hi All,

So I have a few questions for those with some experience with their AP systems...

I believe I understand the nitrogen cycle and how the grow beds (with or without plants) process the ammonia and resulting nitrites. And I understand that the plants use the resulting nitrates. The two bacteria colonies in the grow beds will grow/wane to reach equilibrium with the amount of ammonia coming in from the fish tank. The more fish you have (or really, the more fish-waste you have), the larger your grow beds (or other gravel-beds) need to be to process the ammonia into nitrates, and you need more crops growing in those grow beds to consume the nitrates. It would seem to me that the more ammonia/nitrite-processing capacity you currently have, the faster it can adjust to small changes (like when adding a few fish).

1. So let's say we have a 1000 liter fish tank and 6 10 square foot grow beds (60 square feet total) (I'm just making numbers up here...). To start up this system, would you put maybe 5 fish into the tank with only 200 liters of water, and run that water through one of the grow beds until you have a good bacteria colony working? And then maybe add 10 more fish and another 200 liters and throw some of the grow-media into a second grow bed and start watering both grow beds, and work your way up to "full capacity" in that manner? If so, then I'd need to have a source for fish that will give me just a few at a time, or someplace to hold the extra fish during this process, right?

2. I've read in some posts that people (particularly in cooler climates (like mine)) will turn off the waterflow to their growbeds at night to reduce cooling. It seems to me that you'd never want to do that. Without water, the bacteria in the grow beds will wane (or die altogether), and then I'd be in for some serious ammonia spikes in the fish tank. Am I right in this thinking? It's imperative to keep that water flowing through the grow beds (or other gravel filter), isn't it?

3. In reading the forums, most of you with active systems seem to harvest in "batches." I can adapt my vision for my system to that, but my initial vision is that of a system where the harvest (both fish and veggies) is more of a continuous thing. For instance, Fridays are harvest days -- one fish and a bowl of vegetables per week (granting that there will be more bountiful weeks than others). Are there folks doing this kind of operation? Any special considerations to be aware of?

Regarding capacity... It seems that the more fish you put into a given-sized tank, the more grow bed and plant growth you need to process the fish waste. Having less grow bed processing more fish waste will produce more nitrates, making the plants grow better (is that true?). But if you push your capacity too far, any little thing can be potentially disasterous. It makes sense to have extra processing power available (more active grow beds than you might need -- spreading the processing out so it operates at less than 100% capacity). So I realize that these numbers that float around (like 1:1 tank-size to grow-bed size, or 2:1, or whatever) are pretty poor guesses. The real number has to take into account the amount of fish waste (which is directly related to the amount of feed), the area and to some extent, the depth of the growbeds, how much light is on the growbeds, the temperature of everything, the water flow, etc. etc. It would seem to be *most* productive, you'd want to use the smallest amount of grow bed to adequately process the fish waste. But the closer you pack things to capacity, the more fragile the overall system will be.

4. I believe if your system is working, there will be 0 measurable ammonia, 0 measurable nitrites, and near-0 measurable nitrates (right?). How do you know whether you have more capacity or not? As you grow the system, does the time it takes to reach equilibrium give a clue as to how close to maximum you are? How do you determine where you are in relation to the maximum, and how do you determine how far below capacity you should stay for safety? How can you predict fluctuations in your processing capacity?

Thank you,

Brian

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Hi Brian,

I believe I understand the nitrogen cycle and how the grow beds (with or without plants) process the ammonia and resulting nitrites. And I understand that the plants use the resulting nitrates. The two bacteria colonies in the grow beds will grow/wane to reach equilibrium with the amount of ammonia coming in from the fish tank. The more fish you have (or really, the more fish-waste you have), the larger your grow beds (or other gravel-beds) need to be to process the ammonia into nitrates, and you need more crops growing in those grow beds to consume the nitrates. It would seem to me that the more ammonia/nitrite-processing capacity you currently have, the faster it can adjust to small changes (like when adding a few fish).

You're essentially correct but grow beds are not the only way to achieve nitrification. You can use other types of bio-filters, too......including trickling filters and moving bed bio-filters.

Obviously, grow beds are very useful because not only can you use the plants to harvest the nitrates but you also get to eat the plants.

Trickle filters are much easier and much less expensive to set up......so they can be used as supplementary bio-filtration when you need it quickly or to provide a little extra protection when required. They start up quickly (particularly if added to an existing system), too.

1. So let's say we have a 1000 liter fish tank and 6 10 square foot grow beds (60 square feet total) (I'm just making numbers up here...). To start up this system, would you put maybe 5 fish into the tank with only 200 liters of water, and run that water through one of the grow beds until you have a good bacteria colony working? And then maybe add 10 more fish and another 200 liters and throw some of the grow-media into a second grow bed and start watering both grow beds, and work your way up to "full capacity" in that manner? If so, then I'd need to have a source for fish that will give me just a few at a time, or someplace to hold the extra fish during this process, right?

Personally, I'd skip the fish initially. I much prefer fishless cycling.....as described here. It doesn't put fish at risk, it's faster and more decisive.

If you're determined to start with fish, fill the system with water and get it circulating.....and then add the fish as you've described. The important thing is to test your water as you go.

2. I've read in some posts that people (particularly in cooler climates (like mine)) will turn off the waterflow to their growbeds at night to reduce cooling. It seems to me that you'd never want to do that. Without water, the bacteria in the grow beds will wane (or die altogether), and then I'd be in for some serious ammonia spikes in the fish tank. Am I right in this thinking? It's imperative to keep that water flowing through the grow beds (or other gravel filter), isn't it?

If you have the ability to isolate the grow beds......and this should only be done if you have mechanical and supplementary bio-filtration.....you can safely minimise the overnight heat loss. Just shutting the system down is dangerous......and low dissolved oxygen levels will probably kill your fish before high ammonia levels will.

3. In reading the forums, most of you with active systems seem to harvest in "batches." I can adapt my vision for my system to that, but my initial vision is that of a system where the harvest (both fish and veggies) is more of a continuous thing. For instance, Fridays are harvest days -- one fish and a bowl of vegetables per week (granting that there will be more bountiful weeks than others). Are there folks doing this kind of operation? Any special considerations to be aware of?

You can do it either way. Most of those who grow batches do so because they are growing to a specific season......trout for cool weather.......barramundi, tilapia, jade perch for warm weather.

You can start harvesting individual fish as soon as they are big enough to eat. You may even start off eating two smaller ones until they get big enough to become a single serve.

If you are in a climate that is fairly stable year round (like the tropics).....or if you have a means of controlling your environment (like a greenhouse), you can grow indefinitely or at least extend your growing season.

Regarding capacity... It seems that the more fish you put into a given-sized tank, the more grow bed and plant growth you need to process the fish waste. Having less grow bed processing more fish waste will produce more nitrates, making the plants grow better (is that true?). But if you push your capacity too far, any little thing can be potentially disasterous. It makes sense to have extra processing power available (more active grow beds than you might need -- spreading the processing out so it operates at less than 100% capacity).

Think in terms of bio-filtration (rather than grow beds) for greater flexibility.

The more fish you have.......the more feed you use......the more waste you generate.....the more bio-filtration you need.

You're right. If you're right up on the upper limits of your system's capacity, it only takes a single small thing to turn it into crying time. Even if you're running a modestly stocked basic flood and drain system, it only takes a convergence of small things to produce a fish kill.

Your system should be designed to maximise nitrification and aeration while minimising those influences which deplete oxygen in the system.

So I realize that these numbers that float around (like 1:1 tank-size to grow-bed size, or 2:1, or whatever) are pretty poor guesses.

You're right......they are next to useless without heavy qualification.

The real number has to take into account the amount of fish waste (which is directly related to the amount of feed), the area and to some extent, the depth of the growbeds, how much light is on the growbeds, the temperature of everything, the water flow, etc. etc. It would seem to be *most* productive, you'd want to use the smallest amount of grow bed to adequately process the fish waste. But the closer you pack things to capacity, the more fragile the overall system will be.

When it comes to grow bed media, the only number that is truly important is the overall volume of the media (and the resulting surface area of the media). How deep it is is of no consequence whatsoever.

4. I believe if your system is working, there will be 0 measurable ammonia, 0 measurable nitrites, and near-0 measurable nitrates (right?). How do you know whether you have more capacity or not? As you grow the system, does the time it takes to reach equilibrium give a clue as to how close to maximum you are? How do you determine where you are in relation to the maximum, and how do you determine how far below capacity you should stay for safety? How can you predict fluctuations in your processing capacity?

It varies quite considerably. Ammonia can range between 0 and 0.5......Nitrites should be 0 - 0.25.....and Nitrates can vary between barely detectable and up into the hundreds of ppm.

If you have more nitrates, you have more growing capacity.

If you run your system with the idea that you are in the water management business......testing regularly and reacting to the test results in a timely manner.....you won't go far wrong.

If you run your system at full throttle, you'll discover that, when things go pear-shaped, it happens very quickly. As you acquire experience, you'll get more of a sense of what's possible.....so start off slowly learn as you go.

Gary

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I'm new but can offer some help. To the 1st question, you need to read up on cycling your system. I didn't do it with my first system and everything went fine, but with a larger system able to hold more than a few goldfish, I would. They don't start the system with fish all of the time, sometimes they use other things which can help get the bacteria culture started, so you don't end up killing the fish you have. Those down in Australia use a product called seasol, but from what I've read you can actually pee in the system to get that ammonia started. Don't pee in your system though if you are on medication, that can be a problem. :D

I have a small system and have planted lettuce. Plant leaf varieties and you can harvest at will when ever you have the need. Just pluck off leaves that are on the outside of the plant. I really like the ideas of using plants that you can harvest a bit at a time, but some veggies will need to be harvest all at once, but you can still stagger the planting of these.

Theres some help.

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well done gary

lots of questions

i am only in my second year with 100 rainbow trout but i have noticed with my oldest GB that the growth is very dependent on the temp ( my water gets down to 8 celsius in winter and 25 in summer) . same as soil gardens

also my older beds (last years )produce much better than new beds with little affect from fish waste

probably the build up of gunk in the bed

as far as harvesting goes, i fill up my grow beds with all sorts of things , I struggle to find a spot to plant things generally. and just go out and pick whatever is ready for our dinner

i get a bit of silverbeat ,onion , radish snowpeas chives etc most days

just a mix and we dont go shopping

if it was commercial it would be different but its not

also the fish , well i'll just ask my wife if she wants trout for dinner tonight. ....... she said yes so thats the fish harvesting covered

i rarely check ammonia levels, now and again as i am increasing the feed at this time of year

i started out with one ft sump and gbs

now have added a swirl filter, settling tank and biofilter/up down thingy and soon to add a trickle filter which will help keep temps down when the water temp starts to get too hot for the trout

so whatever you do may i suggest leaving your design open to add any of these into the system if you decide you need tham ata a later date

many people do and have to totally rebuild their systems to add the extra filtering components

as gary said in the water management business

have fun

robin

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Thank you for the replies!

Gary... So are you saying that, when loading up a system, the ammonia and/or nitrites and/or nitrates will rise off of 0 a bit when you are approaching the limits of your system? I was afraid that the system might grow to handle the load right up until it couldn't anymore, at which point the ammonia would rise quickly. I like the idea of having a trickle filter running that could take additional load when necessary -- I'll build that into my plans.

What would be a reasonable way to estimate the size of things? Ideally, I'd like to harvest one fish a week. What would your recommendation be for a tank size and grow beds? I expect to use Tilapia in a tank within a heated greenhouse. The answers to these questions will dictate (within reason) the size of the greenhouse (yet to be built). I know that many have built systems, then rebuilt to expand/change their systems. I'm hoping to take advantage of such experience in estimating my space requirements. I don't mind changing things around, but once the greenhouse is built, I will not be able to change the structure of it.

Thanks,

Brian

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Hi Brian,

Gary... So are you saying that, when loading up a system, the ammonia and/or nitrites and/or nitrates will rise off of 0 a bit when you are approaching the limits of your system?

You might get minor fluctuations in ammonia even when you are not right up on the governor.......your fish might stop eating for a few hours or you may be a day or two overdue for a filter clean, for example. Some systems will evidence traces of ammonia all of the time......particularly if they are carrying a reasonable fish biomass.

I was afraid that the system might grow to handle the load right up until it couldn't anymore, at which point the ammonia would rise quickly. I like the idea of having a trickle filter running that could take additional load when necessary -- I'll build that into my plans.

If you exceed the bio-filtration capacity of the system, your ammonia levels will rise. Unless you're changing something dramatically (or you experience a bio-filter crash), it will usually occur gradually. It's better that you keep it at the trace level.....by adding more bio-filtration (assuming you haven't designed your system for a given (sustainable) feeding rate) in the form of trickle filters or grow beds.

.

....I'd like to harvest one fish a week. What would your recommendation be for a tank size and grow beds? I expect to use Tilapia in a tank within a heated greenhouse.

One approach would be to say that, at the rate of 1 fish per week, you are going eat around 50 fish per year.

What size? For the purposes of the exercise, let's assume we're going to harvest at 1lb (around 450g). If we assumed that you would grow and then harvest a full year's crop of fish, you would, at the time of harvest, have about 50lbs of fish in the tank.

They would be eating, for example, about 3% of their body weight in feed each day = about 1.5lbs of feed per day....at the time of harvest.

Your system would need to be designed to cope with the waste generated by that amount of feed in that number of fish.

What your system looks like from this point will depend on a range of factors.....including the available space, the number of grow beds/tanks (or other bio-filters) you plan to use....and some other factors, too.

You can grow 50 tilapia in a 1,000 litre tank.....or less. The size of the tank isn't the most important factor......it's how you plan to deal with waste generated by the amount of feed that it will tank to grow those fish.

If you want to grow quickly (and sustainably) then you will need mechanical filtration......and, even if you decided to use media-based grow beds, I advise you to use supplementary bio-filtration, too. There are a number of benefits to do it this way.

The answers to these questions will dictate (within reason) the size of the greenhouse (yet to be built). I know that many have built systems, then rebuilt to expand/change their systems. I'm hoping to take advantage of such experience in estimating my space requirements. I don't mind changing things around, but once the greenhouse is built, I will not be able to change the structure of it.

Get your head around how you'd like to approach it all.

Read some more......ask some more questions and get a sense of why people do what they do.

Some people are more interested in fish while others mainly want vegetables. Some people want to grow fish in tanks but like soil-based growing systems for their plants.

Gary

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