Replacing ro/di filters etc

[mark]

Probably the best indicator is TDS and consider rejection rates for the membrane and Aquasafe's recommendations (900g life (or every 6 months based 150g/month)). Vague answer I know, but again in my case, had single digit TDS forever, then I get 20. Been using a year, evaporating 1-2 gallon/day plus water changes, a year seems reasonable at least for me.

Aquasafe filter changes in their instructions towards bottom.

Aquasafe's site has prices. Problem is they don't sell individual changes and recharges but years worth. I was lucky in Edm was able to split an order.