I've had my system up since June 1st. It ran a few days before June 1st, but on June 1st is when I added the plants. A few days after that I added the Goldfish. I have a 50 gal tank and I first I had about 4 Goldfish in there (about 2 inches long) Everything seemed to be going good. Then one fish would die, then later another etc. So then I started to keep about 6 in there. Same thing happened, the fish would do good for about a week and then they'd slowly start dying. Then I got down to 2 fish, So I went and bought 10 more yesterday. 2 have already died.
The dead ones look like nothing is wrong with them, they show no signs of disease or anything like that. They were swimming fine and then the next morning dead. I have been checking my water. I check pH everyday and then about once or twice a week I check all of it. I was checking all of it almost everyday, but now I do once a week-ish. My water labs really don't seem to be changing much. My pH stays around 6.8 - 7.0. Nitrites stay at 0 or one time they were at 0.25. Nitrates stay at 0 and ammonia stays at 0, with 2 times being 0.25. This morning 2 fish were dead, I checked my water levels. And pH was 7.0, and everything else was 0.
Also my Roma tomatoes are trying to get Blossom End Rot, so don't know if that has anything to do with it or not.
are you using tap water with out letting it stand for 24 hours to let the chlorine to off gas. Also are you using feeder goldfish?
Hmm... goldfish are pretty hardy. We started out with six in our indoor system and when they grew to baseball-size, moved them outdoors to the sump tank. That was a year ago and we haven't lost one. We now have six more indoors and they're perky as can be.
Do you have enough oxygen in the water? I suggest adding a pump and air stone so that you are not relying solely on return water for oxygen that way if you have a mishap with your return water, the fish will be getting oxygen from a different source. You'll know the oxygen is low if the fish all hover near the top of the tank, gulping at the surface--that is, if you catch it in time. We keep air stones in our indoor tanks, our outdoor sump tank, and our main fish tank--I believe you can never over-oxygenate the water.
Also, are these feeder fish, or the standard fancy pet goldfish? Feeder fish (and minnows) are usually on their last fin and it's not surprising they all went belly up. But the pet grade goldfish should be pretty lively and tolerant of some less than perfect water conditions.
Try the air stone; I have a feeling that will be a big help.
If you already have an air stone, and you've been letting the water off-gas, I think the issue is the feeder fish themselves. They're feeder fish because they are in poor condition to begin with; they're not expected to have much of a lifespan. Get some of the "fancy" or pet-grade goldfish--calicos, black moors, etc. Those little guys are hardy and should be around for a long, long time.
Phil, I'd check with your local water services and see if they add any other chemicals to the tap water. I live in Nebraska and they add chloramine to ours, which means if you want to use tap water you have to put a chemical in it to remove the chloramine. I just use rainwater and in the winter I get the filtered water at the local store. Chloramine will prevent the gills from extracting oxygen from the water. I have six goldfish that are about 6-8 inches long now that started as tiny comets. They aren't the initial six that I started with though, I lost all but one when my ammonia skyrocketed... that's a time I refer to as the aquapacalypse. Once I balanced the ammonia I haven't lost another, after replacing the 5 that died.