Hi,
I know that water quality can become really bad if you use hairsprays or scented candles in the house. Even one use affects the water a lot. I'm not a specialist with water quality, but my tank has really good ones and my husband who's got education in these matters says no hairspray or scented candles. I sprayed once hairspray in the bathroom, far away from the tank and opened the window afterwards. In the evening the tank water had a film on top of it. And it happened again so I realised how easily these things affect the tank. Not sure if this helps any, but I thought I'd mention it.