Question for Oliver

[aquahealth]

Hi Oliver, I see you have an awsome amount of experience with aquaponics, and I've read your 101 info. I'm trying to get started and would like your feedback please as I am simply not able to do the figuring even as good as all your writing is.

I am planning four flood and drain beds, 4'x8'x12" using pea gravel, and I understand that each bed would hold 96 gallons, considering the gravel, for a total of 384 gallons. And a 6' diameter round 2' deep uv protected fish tank that holds 320 gallons.

I am planning on using the type of gold fish that only get to be about 3 or 4 inches.

As far as the tank sizes go, does it sound like it will work out good?

I am planning enough sump tanks for the flow, and these will hold duckweed and floating rafts.

In my system, I am planning on the fish tank level to remain the same at all times. So my last question is, when sizing the pump, shouldn't I only go by the gallons in the grow beds, x's 4 cycles an hour, and with a bit more for elevation?

Thanks Oliver, Bill.

[Oliver]

Bill,

First, I want to open this question up to anyone on this forum who wants to chime in.

A 4 X 8 X 1 foot grow bed translates into 32 cubic feet or 239.36 gallons each. So, 239.36 X 4 equals 957 gallons of total grow bed container volume.

As a bio-filter, it can support about 100 pounds of fish, more if you feed them less than growth amounts of food.

100 pounds of fish in a 320 gallon tank can be considered high density. The main problem with high density is that the system can be unstable. Things can change rapidly and that is problematic. If, on the other hand, you keep the fish density low, the system is more stable but at the same time it takes longer for the nitrates to build due to the amount of water in the system.

Then there is the problem of growing area per pound of fish. If you are operating high density, then you can grow lots of leafy greens and a few flowering plants once the system is mature. If you go with low density, then the flowering plants may not be an option. Over planting for the amount of fish, fish waste and therefore nutrients in the system will cause reduced plant growth and lots of roots in search of nutrients clogging your beds and getting into your syphons.

Duck weed absorbs ammonia directly as well as absorbing nitrates. As it is a rapid growing plant, it can remove large amounts of nutrients from the system leaving less for the other plants.

Overall, I see an imbalance in the amount of planting area, including the duckweed and rafts in the sump tanks, and the grow bed area for the amount of fish that are needed to support that amount of vegetation. You have 128 square feet of grow bed planting area alone, and that requires 64 pounds of fish for leafy greens and two to three times that it you add flowering plants, let alone the sump tank growing area.

I am not sure how you are going to plumb your system with the constant height of water in the fish tank but is important to make sure that all the fish waste go through your pump in order to macerate the solid waste. This is important in order to increase the solid waste surface area so the Heterotrophic bacteria can mineralize it efficiently.

For all the bio-filtration you will need ample aeration. This can be accomplished in the fish tank if you move your water through your system rapidly. Adding aeration to the sump tanks would be a plus.

As to the water pump, I would size it to exchange the water in grow beds 4 times an hour. Assuming about 400 gallons of water in the grow beds, that works out to about 1600 gallons per hour. Oversize the pump as that rating might be at zero pressure. I would say that a 2000 GPH water pump should suffice.

If you have the room, I suggest you adding another fish tank of the same size. It is alway best to have multiple fish tanks if you plan on breeding and raising your own fish.

Oliver