beginner setup

The hang on the back of the tank powerfilters are very easy to install and operate. Just make sure you get one that is rated at more gallons then the tank. I personally use 2 of them on my 55. one at each end does a nice job. I am a big fan of using 2 filters on one tank. If something would happen to one like a breakdown there is still one running until you get home and find it. alot of people like the aquaclears. I started just using the ones made by tetra they are still running today and a little cheaper then the aquaclears, that is up to you. Good Luck!!

It doesn't make much sense to decide on filtration before you figure out what fish you'll keep and how heavily you'll stock those fish.

In your water, you should be able to keep most fish. You could go with some of the smaller and more docile african, or you could go with a couple of angels, a school of cardinal tetras and some cory cats.... the possibilities really are endless.

Once you figure out what fish you'll keep, then we can make specific filter recommendations. A couple of HOB filters are generally easiest; Aquaclears and Emperors are two popular brands. If we know what fish will be in the tank, we can make some good filter suggestions.

Jim

As stated, the possibilities are endless concerning what species to go with. Since you are fairly new at this, I would suggest less expensive fish. There are plenty out there and they come in many different shapes, colors, etc....
Try to pick fish that generally occupy different "zones" of the tank. That is to say that you want fish that primarily dwell at the top, those that prefer the middle, and some to occupy the bottom of the tank. Fish can and will swim all over but if your fish generally occupy the different levels of the tank, your tank will look more full with less fish and the fish won't be stressed trying to compete with everyone else for a little space.
Another point, fish can tolerate a wide range of water parameters. I say this b/c most tetras prefer acidic waters which may lead you to believe you can't have them. You can as long as your water isn't extremely alkaline (which you've already stated it isn't) and you slowly acclimate your fish to their new water. Chances are that the local fish store (LFS) isn't taking extreme measures to provide the exact water conditions as the fish's natural environment and (if you and the LFS are on public water system) they're using the same source of water as you.
I agree with the filter suggestions and would suggest Aquaclear (no comparison exp. here, it's just what I've always had!) and either go with one AC500 or two AC300's. I started with one AC300 on my 55gal and later added another.
Keep researching and your decisions will become clearer. If not, ask more question!

A Vote for Gold Fish

Let me suggest goldfish (GF). They are hardy, accomodate most water parameters (and yours sounds fine for most fish), they are easy to find, not expensive, come in a wide array of colors, are easy to feed, and are easy to keep.

When I say GF, I am referring to most of the fantail varieties (these have split tail fins, so they have two fins, which billow gracefully in the water). There are some exotic hybrids that you won't find in your general fish stores that I'd avoid (celestials, bubble eyes) but for you money the fantails are great.

Filtration is an issue for GF -- they are notorious poopers. Lots of good types are out there, and you'll find a huge range of opinions here concerning them. Basically, everything works for someone, but I haven't heard anyone say anything bad about Aquaclears. Two AC 300s should be plenty for a 55 gallon tank. I also use bubble wands in my GF tanks. The bubbles themselves do not put oxygen in the water so much as they provide surface agitation which allows the bad gases in water to pass out into the atmosphere, and that is a good thing. A little air pump with an airstone will help and it provides an interesting focal point in the tank.

GF do not need heaters, so you can save a few bucks that way.

What I like most about goldfish is that they inhabit all the zones (or strata) of the tank. Some fish live on the bottom and others hang out up top. I find that boring. GF are all over the tank, so for your tank you'll have a lot of fish activity, and isn't that the reason we keep fish anyway? You can't pack a tank as densely with GF as you would other fish, and GF tanks, since you don't need to heat them, are usually single species tanks. For a 55g I'd think 5 or 6 fantails would do nicely. Avoid koi for an indoor tank.

GF are easy to feed, and I've always used pellets as opposed to flakes. If a pellet sinks, the GF will find it on the bottom. I see no reason for a fish to eat at the surface and gulp air if it doesn't feed so naturally.

Any other questions about this fish, which I am so obviously biased in favor of, just ask.

Regards,

Val