Supplementing the other mailings:
There is not only this one test kit. Unfortunately, these tests are not supported by the aquarium companies; for them such tests are too complicated and not necessary because most usual aquarium fishes live in highly infested aquarium waters quite well. But it’s different with blackwater organisms as Paros are.
A very good test kit which I have used often with veery informative results is the “Cult-Dip-Combi” by the famous German Merck corporation (10 culture media dip-slides for the colony count of bacteria, yeasts and moulds, the can be stored quite long a time at temperatures between +15 to +25 degrees Celsius (protected from light). The product number is 1.00778.0001.
Look for the internet page of Merck and enter the name of the test. It may well be that in the meantime they have developed newer test kits that I have not seen and used hitherto, and there may be other companies with similar products. Merck is a forerunner and foremost developer of high quality products in that field. The principle seems to stay always the same, however. And there are suppliers of the Merck-products in other countries as well.
It is certainly advisable to keep a Paro-tank not sterile but free from the huge amounts of germs that live in normal aquaria. Therefore it is advisable to remove all decaying materials as soon as possible, for instance inconveniant wood or older decaying leaves. Dry Terminalia catappa-leaves, for instnnce, are of high value, but after some weeks they become a source of the opposite processes and must be removed or substituted by new ones. The same holds for older alder cones.
Use such a test like those recommended with a normal aquarium. It might look splendid and clean and a nive underwater garden, but you will be frightened by seeing the thousands of germ nests on your testing unit!