fish died

Question
QUESTION: Last week I purchased a f8 puffer and a pleco for my 46 gallon.  I haven't had fish in it for a while, but I made sure the tank had cycled before adding them.  Well the pleco was doing fine.  However the f8 would not eat no matter what I offered it and it died yesterday (only 5 days after purchase), now today when I came home the pleco was dead on the bottom of the tank.  I have tested the water and ammonia levels are 0.  All other levels are also in range.  Is there something wrong with my tank?  Any recommendations before adding new fish again.

ANSWER: what where the other water chemistry results??? how warm is the tank???  what are you feeding the fish??? dave

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QUESTION: the nitrate is o, nitrite 0-.5, ph about 7.5, kh 120-180, and gh 120.  The thermostat was reading around 76 yesterday, so I did adjust the temp; it now reads 78. (I am now realizing this may have killed my pleco) my f8 was already dying.  I have fed the fish everything trying to get the f8 to eat (flake food, shrimp pellets, tubifex worms, algae disk and freeze dried krill.) I did remove the food from the tank when it didn't eat.   do you think the temp changed shocked the pleco?  If so is it safe to try a couple new fish.  I don't think I'll get any more puffers...I didnt realize they were brackish, since the pet store sells them as fresh.  What do tou think of angels, what other fish are compatible?  Thanks for all of your help.

ANSWER: It is hard to say what killed the pleco... they are usually hardy... most die in the home aquarium from starvation. I would try something like platy's for the next fish you try.  They are pretty hardy... If you can keep the platy's alive then I would try angelfish.  The other possibility for the fish death may have been something that doesn't register on the water chemistry panel.  Sometimes household chemicals can get into the tank... things like Windex, etc.... and kill the fish off... dave

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QUESTION: New problem.  I have a 75 gallon tank that was cycled at the same time as the other above.  I purchased fish for it at the same time as well.  I bought a pleco and a red bellied pacu.  Today when I checked on my fish the pleco was upside down on the bottom.  He is still alive but his fins look almost shredded.  DO you think the Pacu has been harassing him and caused him stress or might there be some other issues.  The water levels seem to be perfect with no ammonia and nitrites at 0.  I have since moved the pleco to my other tank and he seems to be eating.  Are there any steps I can take to keep him from dying.  Are there any compatible tank mates for the pacu, as I now realize that my tank is going to be too small for him full grown, will he do okay by himself?

Answer
Pacu... they are related to the piranha... I think it probably thought your pleco was lunch.... They are very odd fish and they grow to be 2-3 feet long.  The bigger they get the more unattractive they are which is sad because then they are small they are really nice looking fish.  If your pleco is eating he will probably be fine... I would put some salt in the tank and keep your eye on him.  Make sure you are feeding him plenty of greens such as algae wafers, zucchini slices and maybe some frozen green peas.   dave