Putting Growbed into fishtank

[Gary Wong]

This is more of an "aquarium" question, but I wanted to post here because I'm mainly an "aquaponics" guy and it seems aquarium folks are very anti-no water changes.

In my aquaponics system I've never changed the water, 1 year running.  Everything is fine.

I just bought a 55 gal aquarium and wanted to see if I could minimize water changes.  My thought was to attach a growbed next to the filter hanging off the side of the aquarium, inside the aquarium.  There would be 2 inches of so of dry media on top.  Drill some holes in the growbed and fill with hydroton.  Growbed would just have pathos ivy or some other easy to grow plant.

Question, would this work as a nitrogen remover? Or do I need to put the grow bed in the flow of the water (for example, modify the filters or something)?  I was just gonna have the growbeds in addition to normal filtration.  I guess I'm just not sure if it will remove the nitrates effectively just sitting in the water (but I'm thinking it should).

Thanks for any feedback or thoughts.

[David Palmer]

For the most part, that matches what I just did to convert my 26 gallon aquarium to an aquaponics system.  I replaced the bio-filter with a plastic storage bin filled with lava rock.  To cycle my system, I took my old bio-filter pad and put it in with the lava rocks for a few days. In about 4 days, the rancid fish smell is gone and I'm now enjoying a fresh earthy smell from the aquarium.  I'm not really growing anything yet; just a single basil plant I rescued from outside.

The key is that you need to cycle the water through the grow bed.  Several people have recommended running the full volume of the fish tank through the grow bed about once an hour.  An inexpensive fountain pump works.  Drill holes on the sides to push water into the bed and a hole on the far side for an overflow.  Let the overflow splash into the tank to aerate the water.  This provides a simple continuous flow system.

Someone else did something similar for their school.  They used a large PVC pipe capped at the ends and cut in half length wise as the grow bed.  It's smaller and less weight so you don't damage the glass walls.

To make it a little nicer, add a slow drain to the bottom and a mechanical timer to make it a timed flood and drain system.  I picked up a small filter from the aquarium store to fit over the slow drain; this removes the red cloudy dust from the lava rocks.  This addresses poor water flow across the grow bed so that you don't get anaerobic (no air) regions that will start to smell bad.

From what I've read, nitrates are not poisonous to fish.  It's the ammonia and nitrite levels that can be dangerous.  Bacteria will convert these to nitrates.  The plants grow from the nitrates.  For bonus points, add worms to the grow bed to process fish waste.

[David Palmer]

I found the other system I mentioned,

Thrifty bare bones home system

You might give it a try.  Measure the ammonia and nitrite levels to see how well it works.  Adding worms should give it a boost.  If it doesn't perform well, then start replacing water but at less frequent intervals.

[Gary Wong]

Thanks David, I looked at Amanda's system, looks simple and effective.  It sounds like I can't just touch the grow bed to the water and hope it "sucks" the nitrates out of the water, but rather I need to actually pump the water through the grow bed.    I suppose I was trying to see if I could go pumpless with regards to the grow bed but maybe that's not really possible.  :(