aquaarche,

I see that you have changed from gravel grow beds to a raft system I am wondering why you did that. In doing so, you have eliminated a great bio-filter, one that would process both the ammonia in the system as well as the solid fish waste. Now you have a filter of questionable value (I'm not saying that it won't work) that needs to be serviced regularly.

I am also curious as to how much aeration you have in your system, for it is very important to aerate the water in your fish tank.

From what you wrote, you changed out the bio-filter, added Tilapia, killed off some gold fish and are perhaps wondering what happened. My guess is, and it is only a guess, that you had an ammonia spike that the Tilapia contributed to but tolerated, and the gold fish couldn't handle. Again, this is speculation on my part, as I am not clear on the sequence of events based on what you wrote about on your web site.

Regardless of what you have experienced, I congratulate you on your experimentation. I believe you have, and will, learn much as you proceed with this experiment.

If there is anything I can do to help you, then please ask.

Oliver