Make up water quality

[mudturtle25]

Looking for a definitive water quality spec to achieve for make up water. Understand R/O is a good step, but there is also some "noise" about going the next step to DI. If R/O takes the water down to less than 10ppm TDS, and ph is around 7, is there any reason to add the DI option?

 

[bang guy]

RO has trouble removing the smaller molecules like Phosphates and Nitrates. If your water has a TDS above zero then it probably has some amount of these. They naturally occur but must be managed. If your tank can manage Phosphate and Nitrate then there's no benefit to adding a DI unit. If you are having trouble removing these compounds then DI could be a great benefit.