I'll test the water and post the results as soon as I can. When I first start having problems, my ph was 7.0 and no ammonia. I don't like the test strips either. I favor the liquid test kits because they are more accurate.

There's one thing I'm confused though. I remember having four goldfish, one ryukin and four comets, in a two and a half gallon tank before, then moved to a ten gallon tank, then three irid sharks and four goldfish in another ten gallon tank, and lastly, about six goldfish in a seven gallon tank all at different times. There was no problem with the fish and there were weekly water changes. I don't understand why there are problems now with this ten gallon tank when all the things I did are the same. I had eight goldfish, no other fishes, in the tank for two months with weekly water changes, 25% at least, before the problems started so this confuses the heck outta me. I keep trying to think of the reason why the fish go one by one but I can't think of a reason.

As for the pleco, I remember having one with goldfish before and nothing happened. It lived fine with the goldfish and didn't bother them at all. Was I just lucky? Like I've said, there's a piece of driftwood in the tank for him and I make sure he has food to eat. Some of the flakes fall to the bottom and I know the pleco eats it because I've seen it eating flakes before. He doesn't seem to be bothering the goldfishes at all. Is it just luck?

I'm thinking that I should drain half the water, saving it, and completely clean the tank because I think there might be bacteria in the tank, thus the dying of the fish. I can test the water for ph, ammonia, nitrite, and nitrate, but I can't test for bacteria. What do you think? Should I do it?