RO/DI issue & question

bob · Aug 15, 2011

Hi everyone,

I'm about to put together a new system and wanted to start off on the right foot. I'm making a new batch of water and found my TDS to be a bit higher than it usually is. Right now it's reading about 10, when previously it was 0-3. Is this too high for a mixed reef? What kind of tolerance do you all practice? I have the 200gal mix of ESV salt en route and don't want it to go to waste by using bad water.

Could you also help me figure out where my system is having problems? The system itself is quite old but the prefilters+DI cartridge are about 7 months old; the RO membrane tested @~98% rejection 7 months ago so I kept it. It's been producing near 0tds water since then. I only use about 10 gallons every week or two, so I don't make a ton of water. Here are the current readings:

TDS in (tap): 474
After 3 prefilters: 420
After RO: 16 (96.2% rejection)
After DI: 9

The resin hasn't noticeably changed colors either. Thanks for the help!

jaytizzle · Aug 15, 2011

If you're getting any TDS after the resin, you are probably having resin issues. I can't say for sure, though. Honestly, if my RODI unit wasn't putting out water that read 0 TDS on several meters, I'd look for the culprit and get it fixed. I know this isn't always possible especially in parts of the country where you have higher TDS. My incoming TDS is something on the range of 120-140.

AZDesertRat · Aug 16, 2011

96% is pretty low given your tap water TDS. Just by upgrading the RO membrane to 98% you will double the life of your DI resin without doing anything else. If its not 0 TDS I won't use it since I have no idea what that TDS is made up of.

Spectrapure treats and tests their RO membranes and they test out at better than 98% rejection rate so its worth the $39 for a membrane and matched restrictor as it will save you more than that in DI resin in the first year alone.

If it were me I would also toss the second carbon block and go with a 0.5 micron sediment filter, single 0.5 micron 20,000 gallon carbon block, tested 90 GPD RO membrane and then dual DI filters using the extra caniste for one of them along with your existing one. Tis wil give you guaranteed 0 TDS water for a long long time and the second carbon is a waste of money not to mention additional head loss for the RO membrane so it does not work as efficiently.
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At 7 months you are due and the CSP-DI filter replacement kit contains the 0.5 micron sediment and carbon block filters and a SilicaBuster DI cartridge and the 90 GPD membraneand restrictor is at the bottom of the page.