Wow, where to start...
You really need a bigger tank. I believe that may be a big part of your problem. You should do a complete workup on your water parameters, checking KH, GH, pH, ammonia, nitrite, nitrate, so on. Rays need lots of filtration and super clean water. I would say, that in a tank that small, you would need to do 50% water changes every other day or every third day. That's a lot of bottled spring water. I'm not sure what size your rays were when you got them, but I would think they should be almost twice that size after three years.
Let's start with that.