View Full Version : Phosphate getting through

02/04/2011, 08:44 AM
I'm trying to get PO4 down to <0.01 ppm levels in my reef tank and as a part of that I started looking at the quality of the RO/DI water I use. I'm running a Typhoon with the pre-filter, AWI's 5 and 1 micron carbon filters, and AWI's mixed bed DI. My incoming tap water is around 400 ppm conductivity with PO4 generally around 1.2 ppm as measured by a Hanna low range PO4 meter.

I recently replaced all of the cartridges and tested water quality. The RO water coming out of the unit has conductivity of 12 ppm and PO4 of 0.1 ppm. After the DI cartridge water conductivity is 0 and PO4 is < 0.01 ppm. Looks great to me.

My reef water is pretty consistently 0.05 ppm PO4. Eight days after changing all of the cartridges my reef water PO4 was down to 0.03 ppm. I don't know if this is range of error for the Hanna or true downward process, but it seemed to be moving in the right direction.

Eighteen days after replacing all of the cartridges conductivity on the DI water was at 2 ppm so I checked PO4 on the DI water and it was 0.21 ppm. I replaced the DI cartridge and rechecked water conditions. RO water conductivity is 27 ppm with PO4 at 0.08 ppm. DI water has conductivity of 0 but is showing 0.07 PO4.

Is there anything I should do differently for water treatment to consistently keep PO4 in the DI water down at that < 0.01 level I achieved after changing the carbon cartridges?