Thanks to the friendly advice here I found out about water testing. I bought a test kit today and used it to check the water. It says it tests for NO2, NO3, KH, GH, pH.
So according to the test the parameters are: NO2 - OK, although it is hard to tell with this particular test because the difference in color is only slight. Then, NO3 is between 10 and 25, KH - 6, GH - >21, pH - 7,2.
Despite all the info I've read here and in the lit leaflet it is still difficult for me to conclude whether the water is good for my fish. I have a 40g tank with barbs, an angel, some cories, two ancistruses, a mysterious catfish, lots of teenage applesnails. The cories will go to a new tank soon.
I understand that the water is pretty hard. I have a bogwood piece in there, maybe I should do something else?
I will appreciate any kind advice.[/code]