View Full Version : Phosphate in my topoff water
PDAlber
12/11/2011, 12:11 PM
I have been battling nuisance algae in my tank for a while. Yesterday, I tested the water coming out of my RO/DI, using a salifert test kit, and got a level of 0.1ppm. I went to the LFS and they gave me a similar result. Using my TDS meter, I get a level of 0.01. Does this seem right? Can you have a 0.1ppm phosphate level and 0.01 TDS? The reading came after replacing the sediment filter and carbon block. It appears I also need to replace the DI and possibly the RO membrane (been about a year for both). With a new membrane, fresh DI and carbon, and a new sediment filter, I get 0 TDS. Does that mean 0 phosphate as well? Can you have 0 TDS and still have detectable phosphate in the water?
bertoni
12/11/2011, 05:28 PM
That's a complicated question.
TDS, as we measure it, is actually conductivity. Many calibration solutions are based on the conductivity of NaCL (table salt) and water, but phosphate doesn't conduct electricity the same way an equivalent weight-based NaCl solution would. So 0.1 ppm phosphate solution would measure quite differently from a 0.1 ppm NaCl solution.
There's also accuracy limitations in our equipment. All in all, I'd hope that 0 TDS RO/DI output should have less than 0.1 ppm phosphate. What's the phosphate level in the tap water?
Randy Holmes-Farley
12/11/2011, 06:26 PM
Using my TDS meter, I get a level of 0.01.
What value? Numbers are never less than 1 ppm TDS in any hobby meter.
PDAlber
12/11/2011, 07:52 PM
Sorry, that's my bad. My tds reading is 1ppm.
Randy Holmes-Farley
12/12/2011, 06:58 AM
If that 1 ppm (as opposed to 0 ppm) is from a DI that is becoming depleted, then it is possible to have substantial phosphate in it. Even more than is present in the incoming tap water, as phosphate me be among the first things to be released when the resin has been filled with ions, and new ions continue to enter.
Of course, it might also be testing error. Guessing that on any "odd" test result question that arises is apparently correct here at least half the time. :D
Xx__xX
12/16/2011, 02:36 AM
I recently ran into the same issue. Changed all my ro filters but used the same DI. Still getting .11ppm TDS. Just changed my DI. I will let if run a bit and retest my RO phosphate.
Randy Holmes-Farley
12/16/2011, 06:13 AM
11 ppm TDS is high if it is read inline as it should get to 0 ppm TDS with a working DI, regardless of any other filters working or not. If it is in a collection container, it might just be trace contaminants in that container. :)
Xx__xX
12/16/2011, 05:47 PM
I am sorry I made a mistake in my post. I am getting 0 TDS for a final value out of my RO/DI. But using the Hanna checker I am getting .11 Phosphate out of the ro/di filter. I swapped my DI for new stuff and will test again when time permits.
Randy Holmes-Farley
12/17/2011, 08:10 AM
In general, whether that is accurate or not (it may just be testing error), that is not a lot of phosphate. It is far less than you add in foods each day.
Think of it this way. Suppose you replace 1% of the tank volume each day due to evaporation. That boosts phosphate by 0.0011 ppm phosphate. A single feeding of fish food might add 100 times that.
So don't let the Hanna checker cause you do to crazy things in the name of phosphate reduction. :D
TankRazr
01/18/2012, 01:36 PM
I'm dealing with nearly identicle situation. Tds meter indicates 126 going in and 0 tds coming out. Hanna phophate checker indcates phosphates to be .14.
I'm curious to find a solution. Ill start with retesting.
Randy Holmes-Farley
01/18/2012, 03:42 PM
A second DI is a fine choice if removing this small phosphate input is important to you (and if it is real), but note the post above reminding folks that a single feeding will add vastly more phosphate than this will as top off, and so it is not a big contributor to algae problems or average tank phosphate levels. :)
Switching to a different brand of Di may also be useful. Spectrapure claims some of theirs removes phosphate to very low levels. What brand is the DI?
Randy Holmes-Farley
01/18/2012, 03:50 PM
Here's a link to Spectrapure low phosphate DI. Skip down to the silica buster:
http://www.spectrapure.com/St_replac_p4.htm#Mix
from it:
" They are capable of producing 18 meg ohm-cm resistivity water. They are the first deionization cartridges designed to reduce silica, nitrates and phosphate levels in the low ppb range."
floridascape
01/18/2012, 06:09 PM
I figured this was a good place to pose this question, would my api phosphate test be accurate enough to check the phosphate coming from my ro? I dont see alot of people using api test kits is there a reason for this?
bertoni
01/18/2012, 10:16 PM
The API phosphate kits don't measure down to very low levels, so typically they aren't very useful in most reef tank scenarios.
fishresponse
01/18/2012, 10:32 PM
I also have approx 9-13 ppm in my ro/di water. I have tested this with 2 testers - one inline and one hand held both which give me very close values. Another di cartridge would help get it to 0?
bertoni
01/18/2012, 10:35 PM
I think you should test the tap water level and the level after the membrane to see what's happening. 9-13 ppm after RO/DI is high and might mean something's not working well. The DI cartridge might be exhausted, for example.
mschum
01/20/2012, 10:28 AM
Suppose you replace 1% of the tank volume each day due to evaporation. That boosts phosphate by 0.0011 ppm phosphate.
So don't let the Hanna checker cause you do to crazy things in the name of phosphate reduction.
Thank you so much for this post. I am in a similar situation with my top-off water measuring .05 and it was driving me crazy.
Mark
Randy Holmes-Farley
01/20/2012, 11:23 AM
:thumbsup:
Happy Reefing. :)
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