[goatnad]

RO water is not the problem. I'm thinking your lack of added nutrients is though. Just a random guess.Like key master said no parameters makes it harder to tell what your real problem may be.when posting list as much as you can about about your tank.tank size, filter, lighting, nutrient dosing, plants, fish, gh,kh,ph,co2 levels,ammonia,nitrite,nitrate,water changes and so on. The more info provided the more accurate the diagnosis will be. Is this a dirted tank, liquid fert, dry fert or what?

 

[goatnad]

Because the little bit of nutrients in tap water is alot less compared to the nutrients from other sources like fish waste, liquid or dry ferts, or nutrient from the substrate be it things like organic soil or soils like eco-complete. There are many experienced hobbyists that use only RO but they add nutrints anyway so tap water nutrients isn't needed.