Lowering TDS

NDReefer · 03-14-2008, 08:49 PM

Hello,

I have a 240 gallon reef tank that has recently developed a problem with diatoms. I did some research and found that diatoms feed off of silicates, once the silicates are gone the diatoms are gone. So I went out and got a TDS meter and started testing water. My city water is pretty bad having a TDS reading of right around 1000ppm. I then tested my RO/DI water and noticed it was right around 200ppm, which I think is still too high. I recently bought a change of filters for my Kent Marine Hi-S 60gpd and tested that water. The TDS reading did go down but not as low as I expected, it dropped to about 30ppm. I have read that other people change their RO/DI filters when the TDS reading gets above 0ppm. I also checked on the Kent Marine website and found out that my RO/DI unit is optimized for TDS lower than 200ppm. So my question is can I simply put some sort of pre-filter in front of my RO/DI or do I need to get a new RO/DI system? What are my options for fixing this problem? If I need a pre-filter what kind of filter do you recommend and if I need a new RO/DI what brand/model do you recommend?
Thanks for the help!

***lReef lKeeper*** · 03-14-2008, 08:58 PM

you could add another DI canister just after the 1st one. that should handle the left over TDS that are getting through. it would be a low cost fix to your problem too.

poppin_fresh · 03-14-2008, 10:35 PM

how many prefilters are there on your unit? The fact that changing them dropped your tds from 200 to 30 is a good thing. A perfect membrane with 98% rejection (Dow 75gpd) would get you a minimum of 20 TDS before the DI stage. After Di with such a unit should get you near "0" until the resin gets exhausted.

**Amphibious** · 03-15-2008, 12:21 AM

TDS meters need to be calibrated against a known 0 tds sample. It could be off even if it's new.

Dick

NDReefer · 03-15-2008, 12:33 AM

Thanks for all the comments. I will check the TDS meter, I didn't think of calibrating it since its new. My current RO/DI unit has a total of 4 filters first of which is a 1 micron filter followed by the membrane filter, 0.5 micron carbon filter and a DI resin filter. Do silicates get removed in only the DI filter or are they removed in the prefilters as well?

**CarmieJo** · 03-15-2008, 11:29 PM

I think that the membrane and the DI remove silicate.