What would you do?

[wh33t]

Ok, so I'm having some troubles with my system lately and I can't seem to figure out what I should do next. So I thought I'd see what you guys think.

Imagine this:

Your goal is to start Aquaponic veggies indoors that will later on be transplanted into an outdoor (green house). The outdoor environment will be a series of flood and drain systems in 3/4" gravel with bell siphons. The outdoor fish to start will be gold fish and later on some kind of edible variety, probably Talapia. The kinds of veggies will vary in range from Tomatoes to Strawberries.

So for the indoor portion of it here is what you have.

90 gallon raised pond on casters.
4x8 flood table that is built to drain into the pond.
Big water pump (I think it's an 850gph)

Please tell me what you would do in such a scenario.

[urbanfarmer]

I would use gravel instead of hydroton in the biofilter because it's a) CHEAPER and b) has more surface area.

Anyway. I'm not sure I understand the question. WHERE are you stuck?

The only other thing I would add is make sure that when you plant the initial seeds indoors, try to have a container that can flood but restricts root growth inside a container that can be removed once transplanted. An old pudding cup for smaller plants with a very small hole in the bottom and a few more holes in the top would do it. Consider the plant size and the amount of time it would be indoors, etc.

[wh33t]

I would use gravel instead of hydroton in the biofilter because it's a) CHEAPER and b) has more surface area.

Anyway. I'm not sure I understand the question. WHERE are you stuck?

The only other thing I would add is make sure that when you plant the initial seeds indoors, try to have a container that can flood but restricts root growth inside a container that can be removed once transplanted. An old pudding cup for smaller plants with a very small hole in the bottom and a few more holes in the top would do it. Consider the plant size and the amount of time it would be indoors, etc.

I didn't bother to explain where I'm stuck because I just wanted some fresh perspective on what the more experienced would do.

Currently though I've been having problems with my PH continually plummeting and what I believe to be root rot taking hold in the table which I attribute to the high build up of solids that accumulate in the table.

And thank you for the tip about the roots growing into containers. I never thought of that.

[urbanfarmer]

Try to see if you can add oxygen to those problem spots. It might clear everything right up for you.

[keith_r]

do you have composting worms in your bed? they really do assist in solids breakdown, and love being in the roots
buffering your ph with a long term solution is to add a sock or two full of shell grit... this will slowly bring your ph up... my system has been pretty stable at 7.2 after the first ph drop and subsequent addition of shellgrit

[wh33t]

Try to see if you can add oxygen to those problem spots. It might clear everything right up for you.

I added 2 air pumps that each have 4 air outlets each and spread them through out the flood table with little air stones. It kind of helped the plants a little that were in there but they were responding too slowly and I felt they would surely die so I already transplanted them into little soil pots so I could keep them alive. Mostly just lettuce plants though and it's all an experiment so no real harm done. But I would like to get this working. When the table is fully flooded and begins its drain cycle it's only 4 inches deep... A far cry from "deep" water culture so the air stones don't appear as useful as they would if the table were deeper.

do you have composting worms in your bed? they really do assist in solids breakdown, and love being in the roots
buffering your ph with a long term solution is to add a sock or two full of shell grit... this will slowly bring your ph up... my system has been pretty stable at 7.2 after the first ph drop and subsequent addition of shellgrit

No, my "flower bed" has no medium in it. The plants sit inside rockwool cubes, inside of a net pot with hydroton clay padding them which are then suspended in foam lids, so the roots actually just float. When the table floods they roots are submerged in water, when the table drains the roots are exposed to the air for about 5 minutes.

I do currently have this big gravel "particle" filter which I made which does have a few worms in it but it didn't seem to make a difference. There is still fine particles of fish waste that collect in the bottom of the flood table which collect together to form bigger clumps and then sooner or later the plants roots grow into these clumps and I think that is when the problem of root rot begins. My theory is that the anaerobic bacteria are much stronger in the table where the fish waste settles, that's why we added the air stones.

I should also note, I used to have 90 gold fish in this system. Someone informed me that I should have 3 gallons of water volume for every 1 inch of gold fish. So Now I have about 11 gold fish. They went to a good home though (a friends new tank)

[keith_r]

there are many threads on stocking densities... filtration is the key..
quite a few threads discussing this, but don't use the inch/gallons rules of thumb

[urbanfarmer]

there are many threads on stocking densities... filtration is the key..
quite a few threads discussing this, but don't use the inch/gallons rules of thumb

Yes, inch-to-gallons is absolutely a terrible "rule of thumb". How was this derived I wonder? Can you say a 10 inch fish is 10x more massive than a 1 inch fish or is the difference in mass far more substantial? Indeed, it is. From that example alone you can see how the inch-to-gallon concept breaks down instantly.

We usually try to simplify it by unit mass of fish per unit volume of water, but even this is oversimplified and often inaccurate. HOWEVER, this is a good starting point for a hobbyist because you can monitor your system closely and the potential loss is practically 0 in all cases.

Have fun, enjoy!

[wh33t]

there are many threads on stocking densities... filtration is the key..
quite a few threads discussing this, but don't use the inch/gallons rules of thumb

Yes, inch-to-gallons is absolutely a terrible "rule of thumb". How was this derived I wonder? Can you say a 10 inch fish is 10x more massive than a 1 inch fish or is the difference in mass far more substantial? Indeed, it is. From that example alone you can see how the inch-to-gallon concept breaks down instantly.

We usually try to simplify it by unit mass of fish per unit volume of water, but even this is oversimplified and often inaccurate. HOWEVER, this is a good starting point for a hobbyist because you can monitor your system closely and the potential loss is practically 0 in all cases.

Have fun, enjoy!

I'm not having issues with keeping my fish alive. I'm having a problem keeping my plants alive. If the "inch of fish per gallon" is a poor system of measurement what would you suggest? What about adding/removing fish until the nitrate levels are at 40ppm? or something to that extent?

[urbanfarmer]

No, the nitrates are fine. Flood and drain grow beds rarely have problems with oxygen, but you mentioned root rot... The correct way to calculate the required gallons and relevant surface areas is tedious and unless you already have an understanding of it, it's really too much to post here. Stick with the general "pounds per gallons" and "square feet grow bed per pound" rules of thumb provided by Oliver. The rest will be trial and error for most folks, which is part of the fun; so, enjoy it!

Anaerobic bacteria would cause denitrification, which causes an increase to your pH: 6NO3- + 5CH3OH => 3N2 + 5CO2 + 7H2O + 6OH

Anyway, the shell grit in a removable bag of some sort a great suggestion to adjust the pH problem. Not only will it bring it up, but it will allow the solution (water) to buffer itself.