This hobby is all about keeping the tank water changed out and clean all the time. This is the only way to maintain a stable tank. Hard water is a good thing. Lots of minerals for the plants. What's your water change routine? If you're changing anything less than half weekly, then chances are the water chemistry isn't stable. Small tanks under 20 Gs need a couple of changes a week.
Gradually work up to that 50 percent change, 60 percent is better, that's what I change. The water, fish and plants will respond by balancing the water chemistry and you've solved your tank problems.
"Fear not my child, just change the tank water."