Can someone recommend some good test kits and where they can be purchased at a reaonable price online?
the tetra pond master test kit is really good. and it's pretty cheap as well. I use this one all the time.
Here is a link that might be useful: tetra pond test kit
Good question. Thanks for asking. I needed to know that too.
I would recommend staying away from the test strips (specially the pH type). They tend to be inaccurate and have a rather short shelf-life based on my experiences. The liquid types may be a bit more expensive but have better accuracy, and cost lest per test over the long run. I've had very good luck with Aquarium Pharmaceutical products - an example of a Google search for price is shown below. Whenever I have tested them against published laboratory/research methods they've agreed quite well. The tendency is to buy a kit for testing everything you can think of :-)) but eventually you'll find which measurements ... and how often you'll need to do them ... work best for your situation. Hope this helps.
Here is a link that might be useful: Google search for Aquarium Pharmaceutical pH test kit
Be aware that ALL test kits should be replaced yearly. The regents in them can go bad, making test results inaccurate. You don't need to buy a complete new kit, just replacement regents.
Also be aware that there are two kinds of ammonia test kits. One reads only the unbound ammonia (the kind that can still hurt the fish) and the other reads ALL ammonia, including ammonia that has been rendered harmless by ammonia binders. For most purposes, you will want to use a Salicylate type test kit. Here's a link that describs each type of test kit.
Here is a link that might be useful: ammonia test kit info