Backyard Aquaponics
A place to discuss aquaponics

OK so I was thinking about setting up a small AP system with a 30-50 gallon fish tank and a GB smaller than that because of space issues in my classroom. In order to keep the water clean I was thinking of having a aquarium filter hooked up also because I know the GB would not have enough volume to clean the water.

The question is: will the filter take out the nutrients that the plants need? Or will the filter be OK? What do you guys think?

Thanks!!

Hey HN:
With a system that small it shouldn't matter if some of the solids are pulled out. I don't know what the consensus is regarding nutrients in solution or not in solution - there was some question awhile back about whether the solids need to be close to the roots or whether circulating the water was good enough to get all nutrients to the plants. Not just nitrate which will be in solution but potassium, etc. too.

Most consider growbed size a function of fish, not fish tank volume. So you would simply have to have a less than maximum density of fish in the tank.

Ok, but do you think the filter would be OK for the plants?

With an external cannister filter. Coarse foam at the bottom (inlet normally) then bio material this will merely provide a greater bacterial surface. They normally incorporate a pump. Plants do not require nutrients in solid form and you always get a small amount of small particle bypass anyway. In short with this type of filter the plants should be OK.

With a lower fish density, you wouldn't need an additional filter.

The filter would not hurt the plants, but is not needed if you use a stocking rate based on filter volume, not tank volume. Tam's got it. 4 gal of filter to 1 lb of fish. Or go at an even lower stocking rate if there is concern that students may over feed the fish.

I've tried it both ways. The filter works OK but needs to be cleaned. My growbeds could handle several magnitudes more solids so I eventually turned off the filter and just let the filters do the work. Initially -- before your bioslime builds up, the filter will keep the water cleaner.