Recently lost a Bala Shark, wondering if I'm overstocked.

I've had this 10g set up since June and until this past week, the only losses I've had have been two male guppies (one was already in bad shape and died within an hour of bringing him home) and one female. Recently, we lost our bala shark and there have been several reasons I've considered.

We have three zebra danios that we started the tank with and probably 7-8 immature guppies. The largest guppies were birthed in mid-July and the youngest some time in August. So that's 3 mature zebra danios, 3-4 guppies that are nearing maturity, and 4-5 that are still well under half and inch long. The bala shark was probably 4" long and less than 1" tall and wide. We have a handful of snails, but their population seems to have stabilized.

One of the things that I think may have contributed to the bala shark's death is the difficulty we've had maintaining a constant temperature in the tank. We were using incandescent bulbs until last night and they would cause the water temperature to heat up several degrees while they were on and then drop down significantly when they were off.

I haven't done any water testing, but I add more water weekly and clean the filters then too.

Really? From what I had read and was told at the store (not a chain and the employees know their stuff), my tank was a decent size but that I would have to get something larger as the shark got larger later on. I know that bala sharks do grow much larger, but I figured I could just move him to a larger tank when he grew.

Yes, I cycled the tank with the Danios before putting in the bala shark. None of the guppies are mature, with the oldest being around four months old, so I didn't think that would have affected the bioload as much as something like 8 fully grown guppies.

I've been monitoring the bala shark for a while now and the reason I've been so puzzled about his death was because he hadn't shown any signs of stress. He ate, he was active, and didn't appear nervous.

I'm certainly not adding anything to the tank until I can get rid of these guppies (only one male is even worth breeding), and I'm not fond of the zebra danios either. They're very aggressive.

I think I need to clarify.

I went through cycling with the three danios from June to early July. Added the bala shark and added a male and a femal guppy together two weeks later. The female was already pregnant and she had a fry soon after being in the tank and most of them served as live food.

The male died soon after impregnating the female, the female had her second fry and then died in August or September.

The bala shark just died this past week.

That's pretty much the whole history of my tank and there hasn't been any sudden change in the bioload apart from two birthings. After reading the profile on this site, I'm not going to add another bala shark, but I would like some suggestions for something colorful for after I get rid of these guppies.

Yeah, the danios were actually the only reasons we didn't opt for a nicely-colored betta instead of the bala. I may end up keeping the one surviving male guppy, giving the rest to my parents or to the pet store. My parents won't take the danios because they've had problems with them attacking their other fish in the past, so I'm going to visit the pet store soon and see if they'll take them off my hands.