Over the past week I've lost 1 zebra danio, followed by one of my goby plecos, a platy, then just this morning the other goby pleco just seemed to up and die, was swimming around chomping on algae when the lights came on, came back 10 minutes later and he was flipped over dead. The danio just plain completely disappeared, before that he was acting very strange, not eating anything at all, was extremely skinny looking, could barely swim enough to stay off the ground. First goby plec to die also died quickly. Night before he was swimming around eating algae off the glass, next day when I was doing a water change his half eaten away rotting corpse fell out of my java fern. Both were eating normally right up til when they died. Platy I have no idea what happened, she caught ich a week ago, got over it quickly, other night I looked up after the lights went off from my computer and saw her slumped up on her side in the corner of the tank, she too was acting pretty normally up til then, eating, swimming around fine and everything.
Tested for nitrates, About same as ever, 40ppm(can't seem to get it down no matter what, doing water changes with water with 0 nitrates hasn't lowered it any, done a normal 20% change on Monday and after guessing the danio must have died I did a 50% on Thursday. Water parameters of the new water all pretty much the same as the old water.) ammonia is 0, don't know nitrites. PH is 7.1, Hardness 40ppm, KH 100ppm, temp 78*F 16gallons, set up since January, 4 danios, 2 platies left, one big java fern and a bunch of baby plants, all stuck into rocks, and an anubias nana.
Besides the deaths, my platies other than the one that died oddly enough have been acting really weird, only sitting at the top corner near the filter and heater, away from the lights, whenever the male heads out to try to eat he seems to get absolutely terrified and start darting everywhere really quickly and swimming back to his corner after just a few nibbles of some food or algae. The female isn't that bad but she only comes out from the same corners to eat then sits there the rest of the day. They've been like this about a month now. Only thing's that have changed since then is my having pulled up my java fern from being planted in the substrate and putting it in between a bunch of rocks instead. The rocks are pond rocks bought from home depot that were left to soak for a while first. Other than that, the goby plecos were added a little over a month ago as well, and also I set the lights on a timer so that I wasn't turning it on at all random hours like I'd been. They used to be fed right when the lights go on, now it's usually a bit after most of the time as I'm either not up when they come on or out of the house already. Don't know if any of this could have done anything, I just want to try to get as much help as possible before all my fish die.
One last thing I forgot, there's a bunch of tiny snails in the tank too, as well as a bunch of tiny little white worm things on the glass, could any of them be making the fish sick? They may have come from a water hyacinth I put in there that broke off from the bunches in my pond, I soaked it for a week in fresh water before putting it in but I guess it must have brought them in anyway.