Peterpiper

Hi,
This is in the salty section but is the same for fresh water.
This is just some thoughts I have had and would like to hear the views of others.
When we top off our tanks to replace water that has evaporated, some people use RO, RO/DI or treated tap water.
Now the water we use is not 100% pure, so we are slowly adding more impurities to the tank?
Would this slowly build up and at some point crash the tank?

sirdarksol

Yes. In freshwater, it takes longer than it does in saltwater, but yes, both types will eventually develop too much mineral content if topping off with tap water.
It is even happening with actual water changes, but at such a slow pace that it's not as dangerous.

Peterpiper

I see, so would a large WC say every 6 months, 50-70% be called for?
Or how could we control this?

sirdarksol

The larger the water change, the more you'll be "resetting" the mineral content of the water.
Distilled/RO water for topoffs will fix the issue.