[James Bulton]

When I fit new filters and membranes I test the flow per minute and record this per/ liter reading.When this drops to below 75% of that flow. Its time for new filters. How I check my membranes. It should bring my ppm to at-least 10% of my PPM and most time even lower, but if it climbs to 20% of my tds ppm I need membranes. At this stage my DI is doing the work so its not cost effected. My pure is always at 000 ppm and I will not use more than 2 ppm.  I am sure you all have a system you use, but this might help some new to pure water making.

[andyM]

Pressure gauges on inlet and outlet of pre-filter housing will tell you at a glance what is happening to the pre-filters and when they need changing.
I change my pre-filter every 6-8 weeks regardless.

[Clever Forum Name]

No more than 2ppm?

Blimey your wasting money right there.

Not even bothered with DI at the moment as using 6 - 10 ppm RO water.

Do you use twin DI ?