I found my pleco dead just a while ago. It was my second oldest fish. He was acting oddly the past few days. I'm not sure what happened though. My other fish seem fine.

Sorry to hear that, how long had you had the fish ? As it could be just down to old age.

I'd only had him a few years. I got him a few months after my goldfish, which I got in 2004 I think. So I only had the pleco since the beginning of 2005.

Well that would count old age out as a reason then, how are your water stats ?

The ph is fine, but I'm not sure about the ammonia (I don't have a test kit). I recently just added some new ammonia remover though. If it was the water, wouldn't it affect the other fish? Everyone else seems fine, and I would have thought the pleco would be the last to go if something happened. I always heard they were very hardy fish too. A few days before he died, my pleco would swim up and down the front glass of the tank. He'd even stick his nose above the surface of the water. He was usually hidden, so I don't know why he'd act like this.

What type of substrate do you have ? Also it might be a good idea to test all your water stats

I have mostly sand, pebbels, and some larger rocks for the substrate. Some areas have more fine sand, others have larger rocks. It varies across the tank. I know I should test my water. I'm going to try to get a proper water testing kit sometime soon.

Think it would be a good idea to get one as soon as you can.
How deep is your sand, and do you rake through it every now and then ?

No, I don't rake the sand. It's about and inch or two deep in most places. How would I go about raking the sand since most of it has larger rocks mixed in? Would stirring it with a stick between the rocks work?

Yes that would work fine. You need to rake/stir your sand every so often, you could even use your fingers, you need to move your sand so as to stop it trapping and holding any nasties

Sounds like the ph could be off or there isn't enough dissolved oxygen in the water which could be because of other water parameters being less than par. How often do you do water changes? How much water do you change each time?

I try to change about 15-25% of the water at least once a month. I have a large aerator with three seperate tubes to aerate the water in my aquarium. Two make smaller bubbles and the other makes large bubbles. Also, my current filter hangs on the back of the tank, and usually the water's low enough so the water from the filter drops a short distance down into the tank. I don't see how the oxygen could be a problem.

Try changing 15-25% weekly. I know that will help. Once a month just isn't enough.

Funky is right you need to be changeing your water more than once a month, i change mine at least once a fortnight

Ah geez, this fortnight thing again.