Total newbie needs help/advice

I would suggest an aggressive water change, as you don't know what killed your plec. However, he probably was not comfortable in such small environs. There are many threads here on fishless cycling, and after you change the water in the tank and start over, you should go that route before getting any new fish.

Neons are not good for that small of a tank--they need more space to move around and need to be in schools--something which would quickly overload your biofiltration in such a small space. I would instead suggest a Betta, an Oto, and a Cory.

Before you worry too much about your Ph, check with the store you will be buying the fish from and find out the Ph of their water. Tropical fish are quite adapable and will do quite well in different water conditions-but rapid changes in condition can cause problems and leave your fish open for disease. Invest in a water test kit that ha Ph, Ammonia, Nitrite and Nitrate minimum. HTH, Steve

You should also test your source water that you are using for your water changes. I know where I live it runs about 8.6-9.0 sometimes, it just depends on what the water company is doing to it that month. If you are adding stuff to bring pH down and then doing a water change with 9.0 water...its not going to help.

Double check you decor. Your pH will also be high if you have things like sea shells, coral bits, or calcium carbonate type rocks.

Also, from your post I got the sense that you were a little confused on what it means to have a tank cycled. Cycled is used to describe a tank that has been allowed to establish the necessary bacterial colonies needed to metabolize the nitrogenous waste products excreted by fish. This can be done with fish or fish-less, but it must be done before you can fully stock your tank. If you are not familiar with this look up info on the Nitrogen Cycle in an aquarium - I'm sure there is something on AC about it.

As an additional note: as the water of a tank matures the natural tendancy of the pH is to decrease - so assuming you never did a water change or anything like that on a tank the pH can go from 8.5 to 6.0 with out adding any chemical adjusters.

pH is unstable only when buffers are low, or there is a secondary reaction taking place. For example, the normal production of ammonia/nitrites can impact the pH, as can CO2, and asoftening agents like driftwood. Water, left in a glass, will not change significantly once any gasoff has occurred. Mature tanks with dipping pH are usually the result on inadequate water changes and buffers. The buffers get used up by the various chemicals from fish/plant respiration, and without an influx of buffer, the pH is unstable. This isn't normal, and should be addressed.

However, the use of chemicals (pHdown/up, ect) are not good. Not only are they only a short term fix (they don't address the underlying cause), but they bring with them several additives that won't help your tank.

So, my advice: First, read up on cycling an aquarium. There are several stickies here about the process.

Second: Do a full water change on your tank. Refill using water treated with a product to treat chlorine/chloramines as appropriate.

Third: Select fish that will do well solitary, or in very small groups of 2-3, that stay small. Pleco's don't fit the bill, nor do neons. Maybe a dwarf gouramie or a betta, along with 2-3 smaller cories like pandas.

2-3 Cories in a 5.5 gallon?

IMHO, There would be a lot of water changing involved with that suggestion!

I was thinking of the smaller cories, like the pandas and dwarf cories, which stay right around an inch or so. Definitely not for any greens or bronzes--way too big a fish.

I gotcha. Thanks for clarifying that for me.

Oto is short for otocynclus, a small sucker mouthed fish. Cories refers to member of the corydoras family, and are sometimes called armoured catfish. Check http://www.planetcatfish.com/core/index.htm for more info on both. They are lots of cories--look into pygmy/dwarf, panda, skunks. You will want to get cories that stay smaller than about 1.5 inches in order to have 3--the minimum number for happy cories.