"Out of the tap nitrates are 40ppm or worse if farmers are fertilizing their fields. Furthermore, my water is ridiculously hard.
GH and KH in double digits."
the nitrates are a problem and will always be a problem, doesn't matter what you stock for fish, and it goes without saying but should be said, but you shouldn't drink it either.
What we need to know is,
pH, GH, KH, nitrates of the
tap water.
the same tests after 15 minutes of sitting, does anything drop?
the same parameter measures before and after a
water change = affects on the tank and between water change "aging".
GH and KH below 4 and over 20 degrees are problematic, but is it really problematic? You are managing to keep shrimp and a gourami (gourami being a labyrinth fish, not such a big deal, but shrimp don't like bad water.) if you are running 11s, technically, you just need a nitrate sink to get rid of those nitrates which would be a crazy amount of plants.
Maybe you need a really slow acclimation process to keep what you want depending on parameters, Most all fish are capable of acclimating over time to
water parameters even extremes. Tetras, angels, discus are troublesome with water quality issues, but most fish jsut need enough time to adjust.... but generalization of the situation doesn't paint a clear picture of the issue and can't lead to a solution to correct it.
Maybe you need to rethink the tank set up and do and over under with the 29g, and blow the 29g out with plantings to use up nitrates to supplement the 50g, a nitrate sump and pass the water through the 29g heavy planted tank to remove nitrates for the 50 gallon lighter planted tank, maybe you keep shrimp and snails in the 29g jungle sump to use up some
calcium and the plants to use up
potassium and
phosphates and keep, it becomes a GH dropper as well as a nitrate remover. heavily planted, lightly stocked with small calcium using critters. and your 50g for your fish, after the plants have worked their magic and nitrates are brought down.
If KH is high, pretty sure you could use and acid buffer to lower KH, and it would produce
CO2, which would benefit the plants also, maybe you store water in the 29g heavily planted and lightly stocked tank between water changes, and it does the work of cleaning up the nitrates and lowering GH and KH, and you use 25g of that water for water changes when nitrates are low, and re-top it with high nitrate water again. to lower it before the next water change.
Maybe you need a RO/DI filter and build your water after for the aquariums, but if you do, I have no idea how you manage to keep shrimps currently. if you have 11-12 dGH and dKH, its not a big deal. neither will really affect the fish, unless it's affecting the pH and raising or lowering it depending on what the parameters actually are. barring that it's not a big deal, it's the extreme ends of KH and GH that cause problems.
No way of knowing what the best solution is. without knowing how bad the problem really is. but it really can't be that bad if you are keeping fish and shrimp in it. there is a solution though and I don't think it's really all that extreme of an answer.
