RO/DI Water Showing Phosphates

[layer3switchguy]

Folks,

Just took a sample of my RO/DI water and it's showing 0.01 mg/l using a Hanna meter. I just replaced the membrane and all media in the unit last night, and have about 25g of water run through the system so far. The TDS meter I have attached to the unit showed 0ppm on both the input/output. Is this a normal Phos reading for RO/DI water, or should I be concerned?

Thanks!
L3

[Roland Jacques]

You're getting 0 TDS before and after what? Your DI or your Membrane? (Personally i use a hand held to check TDS i seem to get better readings with it)

Your DI should take care of Phosphates

[layer3switchguy]

Ok, my TDS meter is plumbed in-line with my RO/DI unit, so it shows TDS coming into the DI and then coming out of the DI(I suspect it's bogus, as it rarely shows any TDS coming into the unit, and if it does, it usually registers 0 after a few minutes)

According to the Hanna meter, I'm still getting 0.01 mg/l of phos, but then again, this is within the margin of error for the unit I suspect. Interestingly enough, I have a fresh batch of Reef Crystals I just made and it's showing a whooping 0.13 mg/l of phos!

I've been battleing hair algae, hence my obsession with phos readings in the tank!

[Randy Holmes-Farley]

If you are reading 0 ppm TDS on the effluent, then I expect the phosphate test is just showing background noise and not a real value of 0.01 ppm phosphate. phosphate is among the more easily bound ions in a DI. :)

[layer3switchguy]

Thank you Randy! Much appreciated. Now if I can just figure out how IO claims Reef Crystals to be Phos free, when a 5g batch just tested at 0.13 mg/l!

[Randy Holmes-Farley]

Assuming the meter is giving accurate answers. :D

[drillsar]

did you check if the TDS is calibrated correct?

[Randy Holmes-Farley]

Actually, assuming it is not broken and reading only 0 ppm TDS for everything, calibration does not much impact the zero point. It changes only the slope. So say if 1000 ppm TDS were really reading 900 ppm TDS, then 10 ppm TDS would really read 9 ppm TDS, 1 ppm TDS would really read 0.9 ppm TDS and the 0 reading does not get impacted much at all by calibration. :)

One can easily test this by seeing if it reads 0 ppm TDS in air. :)