That GH would only be a problem with a very few fish that require very soft water, if then. I wouldn't worry at all about the GH. But, now I'm not at all sure what KH you have. If it took 26 drops, with an API KH test kit, you have 26 degrees of KH, very hard, possibly too much for most fish and many plants. But, not all KH test kits work that way. I suggest not using that salt water test kit, and buying an API KH test kit. With a pH of 6.6 it isn't at all likely that you have a high KH.