Adding DI to RO?

[hillegom]

The water most likely will be suitable with your ro unit. How old are the filters? First buy an inexpensive TDS meter.(total dissolved solids). Then you will know the quality of the water before and after the RO. If the tds is too high upon exiting the RO filters, then you need to add the DI filter after the other filters. This would bring the levels down even more. It all depends on the quality of the water in, To how good the water is comming out. I cannot remember exactly what the % of removal is, but somewhere around 90-95%.
So if the tds into the filters is 100, then comming out is about 10.
A tds meter, will also tell you when to change filters.
For sure if you are going to have corals, then use that ro filter and buy a di filter as well.
I am sure someone in Calgary can tell you what the tap water is like in Calgary