Phosphate in my RODI Water?!

vertwake · Aug 27, 2012

I've been having a phosphate problem in my DT.

I've been trying everything I can think of to lower it. I'm running GFO but it wasn't making a dent. Water changes weren't making a dent...seemed to even be getting worse after water change. So tonight I tested my RODI system.

RODI:
Hanna Checker:
Test 1 - Greater than 2.5
Test 2 - 1.5

API manual test: 0.25

DT:
Hanna: .13
API: 0
Yesterday after 20% water change Hanna was .75 (So my GFO appears to be working...)

So obvious questions:
1. How is it possible my RODI has PO4 in it?!
2. How can I prevent it?

jdpiii3 · Aug 27, 2012

How old is the RO membrane? What is your tds after your DI? Have you tested your tap water before filtering? Also try testing some distilled water and see if you get 0 readings from those kits.

jdpiii3 · Aug 27, 2012

If your final TDS reading is zero, then there should not be phosphate in the effluent. A properly running RODI system will remove all of the phosphate. Once your DI filter reaches capacity and your TDS reading rises to 0001, then you need to change the DI filter

vertwake · Aug 27, 2012

RO membrane is 4 mos old. Final TDS reading from the RO unit is 0...I haven't seen the TDS rise at all yet. (It was rising when I replaced it, so I'm familiar with the symptoms.)

I'll try some distilled water tomorrow and see what I get. I have not tested tap water yet.

jdpiii3 · Aug 28, 2012

if your getting a 0 tds I would believe it to me more of the margin of error for those kits. Do you run 2 DI chambers? how do you pack the DI when you refill?
Did you check your mixing container water, or a fresh collection of water straight from the DI output?

Troylee · Aug 28, 2012

jdpiii3 said:
If your final TDS reading is zero, then there should not be phosphate in the effluent. A properly running RODI system will remove all of the phosphate. Once your DI filter reaches capacity and your TDS reading rises to 0001, then you need to change the DI filter

Hate to say it but this is wrong.... A tds meter does not pick up po4 actually... To the op it's time to change your di resin and go from there... I have seen over the last 2 years more and more people adding a gfo reactor to there salt water mixing stations just for this reason... Wouldn't hurt if you catch my drift..

vertwake · Aug 28, 2012

Thanks for the feedback everyone. Guess I'll start by buying some new filters.

Regarding how I pack them...I have a 4 stage Spectra Pure, I just order the refill containers, don't actually pack anything.

Tonight I tested straight from my Filter and I was still getting .42 even with 0 TDS.

Question is, which piece of my 4 stage do I need to replace? Do I need to replace every filter on it?
This is the one I have: MAXCAP RO/DI SYSTEM

AZDesertRat · Aug 29, 2012

You cannot accurately test phosphates in ultrapure water. Trust a god handheld TDS meter such as the HM Digital COM-100 which is 10x more sensitive than most meters are extremely accurate at low ranges. Hobbyist grade test kits and meters will not be accurate. While phosphates are weakly ionized they will register on a good low range TDS meter.

Ask your water utility if they are adding phosphates as a form of corrosion control in the distribution system, if so keep up with your DI replacements and use only Spectrapures SilicaBuster resin.

vertwake · Aug 29, 2012

Thanks everyone, I've got new filters on the way.

kes · Sep 3, 2012

Yeah, hope this works out for you. You can always get a sample purified water from someplace to cross check the readings/test kits.

vertwake · Sep 7, 2012

So I replaced all 4 of my filters, and my Hanna Checker was still showing 0.65 PO4 coming straight out of the RO/DI system. So I also had a chat with the folks at SpectraPure. They assured me that if I have a 0 TDS reading coming out of the RO system there is "no way I can have phosphates" coming from it. I was told repeatedly that my Hanna checker must be off.

So I guess I'm just going to go with it for a while and see what happens.

tampasnooker · Sep 8, 2012

at .65 reading, you should be able to see the color change yourself. is the sample turning blue? the tests look clear to me until a sample is over about .15 and then I can see the blue tint.

AZDesertRat · Sep 8, 2012

The Hanna checker along with hobbyist grade test kits are not designed for testing ultrapure waters and will not be the least bit accurate. TDS or conductivity are you best bets as there are just too few ions to measure with other methods.

Mike&Terry · Sep 8, 2012

Here is an interesting read about phosphate:

Aquarium Chemistry: Phosphate And Math: Yes You Need To Understand Both — Advanced Aquarist | Aquarist Magazine and Blog

Myka · Jun 26, 2016

AZDesertRat said:
The Hanna checker along with hobbyist grade test kits are not designed for testing ultrapure waters and will not be the least bit accurate. TDS or conductivity are you best bets as there are just too few ions to measure with other methods.

This might be a silly question, but would it make for a more accurate PO4 testing if we purposely add ions to the RO/DI water that are known to not contain PO4? Maybe something that is easily found in our fish cabinet or in the house?

Randy Holmes-Farley · Jun 28, 2016

Perhaps, but I do not know what exactly the requirements of the Hanna are.

StinkyReefs · Jan 3, 2022

vertwake said:
Thanks for the feedback everyone. Guess I'll start by buying some new filters.

Regarding how I pack them...I have a 4 stage Spectra Pure, I just order the refill containers, don't actually pack anything.

Tonight I tested straight from my Filter and I was still getting .42 even with 0 TDS.

Question is, which piece of my 4 stage do I need to replace? Do I need to replace every filter on it?
This is the one I have: MAXCAP RO/DI SYSTEM

Same I get 0 TDS but high phosphate that was just cold RODI water tomorrow I’m gonna mix it to 35ppt and 78 degrees to see what I get for phosphate

Planted Reef · Mar 9, 2023

Randy Holmes-Farley · Mar 9, 2023

This is quite an old thread, but if anyone has concerns about phosphate in ro/di water I’m happy to address them. In general, phosphate in 0 ppm tds water is not significant relative to other sources.

Isolatedreefer · Apr 18, 2023

Randy Holmes-Farley said:
This is quite an old thread, but if anyone has concerns about phosphate in ro/di water I’m happy to address them. In general, phosphate in 0 ppm tds water is not significant relative to other sources.

Hi Randy. M friend is having major grenn hair algae issues, with nitrates at 0 and phosphate at 1.72, as tested on a hanna checker. His ro system is delivering 0ppm tds. The ro water itself gets a phosphate reading of 0.23 and after mixing the saltwater the phosphate reading is at 0.43. Do you think these readings indicate that the source water might be a problem and should be addressed, or do you think because his current tank phosphate is 1.72 that we should be looking elsewhere for the phosphate problem?