RO Membrane Question

Itchy Trigger

Active member
I make about 200 gallons of RO water a week for a large aquarium. We're on well water and so I mix RO and well water at a 2:1 ratio, which yields good water for my 500g freshwater CA/SA cichlid tank. Using a couple of 600 gpd membranes and a powerful booster pump, I'm able to fill my 300g reservoir (100g of well water and 200g of RO) in just about 5 hours. Well water comes in at a TDS of about 300 and the output is generally between 5 and 20, which is fine.

I have a 20" x 4.5" pleated sediment filter and then two 20" x 2.5" carbon filters before the booster pump (and then through the membranes). There's an auto flush valve that flushes the membranes for about 20 seconds upon turning on the pump. I tend to change the sediment filters about once every 2 months, but I'm noticing my TDS is still in the range of 60-70 after changing the sediment and carbon filters, so I'm guessing the membranes are just clogging prematurely. I can't afford to replace the membranes every 2-3 months... Would adding a second sediment filter make a big difference here? Or should I replace the sediment filter more frequently? I was hoping to get 2-3 months out of the sediment and carbon filters and at least 12-18 months out of the membranes.

Given all the figures I've provided above, does it sound like I'm going to just have to replace filters and membranes more frequently or might there be something else going on that I'm not thinking of? Thanks in advance for any suggestions or other input.
Ah! I just figured out what the problem was... I send the RO's wastewater outside to the house's drainage system... The tubing was frozen solid outside the house (it's been about 10 degrees here in the Hudson Valley for the past few days) so the path for the wastewater was blocked and it was backing up into the system. Problem solved!