Watery Graveyard

Remember back almost a year ago when we set up a fish tank for the kids. The picture above is from back then. See all those fish. Yea, none of those original fish are alive anymore. One of the mollies got sick and died pretty fast, which we replaced, but then both mollies died maybe a month later. The clown pleco probably made it two months before it kicked the bucket. The dwarf gouramis probably lasted the longest making it almost four months before dying. We've since then gotten lots more fish, all of which have died except for one. We do have some type of loach / catfish type thing in there that hides during the day that's lasted a good while now (easily the longest survivor in the tank). In between we've gotten an iridescent shark that obviously wanted a larger tank and various other colorful fish that have all died. The algae in the tank is out of control, and I've noticed the pH tends to gravitate towards the acidic if left to it's own devices. How acidic I can't tell since the kit I have to measure it only has colors that go down to 6 and it's definitely gotten to at least 6 so it's probably been even lower. Which, perhaps not coincidentally, is also about the time fish start dying (fish deaths usually prompt a pH check, which then results in adjusting the pH). To be honest I thought the tank would have balanced itself out as far as pH goes by now (in the past it's only taken a couple of months for a tank to get to the point where it settles into a reasonable pH range). We've gone through 3 dwarf puffer fish in the past two months (two of which I just found floating in the tank tonight). Not sure what to do about the puffer fish since those were Catherine's (she doesn't know they're gone yet since I just discovered them floating tonight). Last time the puffer fish died I went out and got two more and never told her the original one died. Catherine never even noticed the fact there was an extra one in the tank (but they are rather small, so it's possible once she actually located one she just stopped looking because she didn't know there were any others).