How can I lower the water hardness?
Is there a sera product for lowering the GH level?
this is within certain limits (some hardness degrees) possible with blackpeat granulate (sera super peat). More extensive lowering (e.g. for keeping fish that require downright soft water in Areas with very hard water) is possible only by using a deionizing setup (reverse osmosis or ion exchangers, see below please). Demineralized water purchased in canisters is of course also suitable - in that case the deionizing system simply stands somewhere else and not in your own household.
Is it correct that the water roughly has the same color as tea after using sera blackwater aquatan or sera super peat?
Yes, this is correct and intended.
To be honest, I do not quite like the brown water tint, since I always had absolutely colorless and crystal clear water in the aquarium.
Fish from corresponding biotopes (typically rainforest creeks and pools) actually like this tint, rainforest inhabitants prefer dim light anyway - and "crystal clear" does not contradict using peat, as no cloudiness gets into the water.
I do not want to purchase a reverse osmosis setup for my rented apartment (there is an R/O system in my workplace, but I do not want to transport water buckets to and fro in my car). I also think that purchased deionized water would be too expensive in the long run.
There is also the possibility to use an ion exchanger. These work economically considering their water consumption - the water you pour in at the top will run out at the bottom deionized. However, the resins need to be regenerated from time to time (usually 1 mol/l hydrochloric acid - i.e. approximately 3.6 % - for the cation exchanger and 1 mol/l sodium hydroxide - i.e. 4 % - for the anion exchanger).
If this kind of water softening is not applicable for you, you might consider changing over to fish from harder water (e.g. Lake Tanganyika, many livebearers, etc.) instead.
Dr. Bodo Schnell