R.I.P. :(

Our goldfish died last night. Poor Dorothy, poor Elvis. Here's the story...I HATE cleaning out that fish tank. Hate it. And I'm the only one who ever does it (Maya can't reach properly), so it gets pretty gross between cleanings, what with the green walls and everything. Well, a month or so ago, we went to a comic book shop in Lafayette, and the guy who owned the shop had a plecostomus in the tank with his goldfish. I didn't think you could put them together, because I thought plecostomi needed warm water, and goldfish needed cold water. Well, the guy said they're fine. So I went to the Concord Aquarium on the day after Christmas, but they were closed. So I went to Pet Smart...never a good idea...and asked them. They said that the plecosomus would grow too big for my tank eventually, but if I was willing to get it a new home at some point, it would be fine to put them together. So I did. Well, all appeared well for about a week, but in the last few days, our poor goldfish haven't looked too well. Last night we noticed that the fish looked like their fins were being eaten, and they were kind of white, like they were diseased. Ted noticed that the plecostomus was EATING DOROTHY'S TAIL!!! Then we noticed that Dorothy was dead. :( Muh. So we flushed her. But Elvis was clearly suffering, and not long for the world, so we flushed him, too. Maya was DEVISTATED. So I came in this morning, and looked around, and this is what I found:
-----------------------------------------------------------------------------------
Plecostomus aggression to other fish:
Plecos just love to suck on ailing goldfish, discus, and other fat bodied fish. Avoid adding them together. There is one pet store near me that has about 20 tanks of fancy goldfish. Every tank has a small plecostomus and at any time, half of them are sucking on a goldfish. The employees apparently believe that any damage overshadows their algae cleaning abilities (in other words, they are too lazy to clean off the algae and do not care about the goldfish). My pleco probably killed the two rosy barbs with him even though he was 9 inches long and they were only about 1.5 inches long. Before that he harmed my goldfish. For more on my pleco with goldfish, visit my goldfish page.
-----------------------------------------------------------------------------------

So I killed Dorothy and Elvis by adding that damn fish. I feel so crummy and evil. Poor things. :( So now what...Maya wants to get new fish, but I feel a bit free of the fish tank cleaning at the moment. We could maybe use this opportunity to move the tank elsewhere, where she could reach better, and she could clean it. Also, we could use this opportunity to put something else in the tank, rather than goldfish. I don't know. But that plecostomus is going. He killed our fish. I'm not sure what to do with him. I could flush him, but it seems cruel to kill him when he was just following his evil instincts. I could try to return him, but I don't know if they would take him. I could ask one of the parents at Maya's school, who has a fish store (I think) for his advice. I don't know. Opinions?