What cartridges should I replace in my rodi system when detecting phosphates

[Rockedash]

I’ve been struggling with high phosphates and it seems like my rodi water is to blame. I was wondering what cartridges I should change and what exactly the membrane filter does because I for some reason can’t find what it exactly does. I exchanged my sediment cartridge recently and that’s already changing color so I’m gonna do that one but I’m not exactly sure if it’s something else because even after I changed it out I still had phosphates. Thank you and have a great day!

 

[MarineandReef Jaron]

Each stage of an RO/DI system makes the next stage last longer but each stage is also more effective. If you pumped all of the water through a DI only you could still get 0 tds water but you would burn through resign so fast that you would spend a ton of money.

With this said the DI is the first thing I would replace if you are detecting phosphate.

The sediment and carbon filters basically exist to preserve your membrane. The membrane removes about 95-99% of the pollutants in your water. The best way to test your RO membrane is to measure the TDS IN and OUT. The output is normally 3-5% of the input. If the outgoing TDS is higher than 5% of the source water your membrane is likely going bad.

Your DI is the final polish of the water, but without the membrane removing the majority of the pollutants it would not make economic sense to use only DI Resin. Replace your resin when the color changes or when you see detectable TDS coming out of the DI stage.

As an illustration, my incoming TDS is around 1000 the TDS out of my RO is about 25 so I am getting between 97% and 98% rejection from the membrane. With the DI resin removing the last 25 TDS I have to swap my DI Resign 3 times a year. If you do the math that means that without the membrane my DI would need to remove at least 20 times more pollutants and I would need the equivalent of 60 DI replacements in a year.