Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
GH might indeed be quite high. The API GH test is one of the first to fail because of old age, but that deep indigo color on your test strip confirms that the GH is quite high. KH test strip result looks a bit lower than the 5 degrees that you tested with the API kit, but probably near enough.
Here is a way to make the GH test work with the reagents:
Put only half aquarium water in the test tube (2.5 ml instead of 5) and top it off with distilled or RO water (total of 5 ml).
Then double the test result. (If it takes 10 drops to change color then the GH is 20 degrees.
You might be able to cut that again, use perhaps 1.25 ml aquarium water, then top it off with RO or distilled, then multiply the result by 4.
When altering the mineral levels in the tank, especially lowering them, I try not to drop them by more than 10% at any one time.
So, if the GH is 40 degrees then drop it by no more than 4 degrees, so it would still test really high. A few days later drop it again. Keep doing that, perhaps twice a week. Gradually the mineral level will drop and the livestock can acclimate.
I know this is safe for the fish. Probably just fine for the shrimp, too.