Phosphates in RODI water

[aloonj]

Having had relatively high PO4 reading for some time and cyano and green algae for months, last week I dumped all my RO and Salt water from my mixing station (after testing PO4 there too) and completed a range of maintenance/upgrades:

- Replaced the DI resin which looked close to being depleted (packed in as tight as can get it)
- Installed a booster pump along with high and low pressure sensors and hooked into the auto flush, which has increased the pressure to around 70psi (from around 35). The autoflush kicks in when the pump starts up and the output TDS keeps at 0.
- Refilled my RO and Salt containers completely (90L each) with a total of 180L or so produced last week. The TDS output has remained at 0, although now a week later the resin looks about 50% depleted already.
- Completed a 50L water change (Waterbox 60.2, so 200L tank+sump volume), with about 20L more throughout the week.

Despite all this, the aquarium has maintained just below 0.19 PO4 reading and today I reran the tests on the water station/RODI output only to find pretty much the same as before I did all the work:

Aquarium: 0.19
Salt mixing tank: 0.14
RO tank: 0.13
RODI output (flushed, TDS 0): 0.09
Reference fluid (0.20 mg/l): 0.23

Any thoughts on where I go from here?

Membrane age: 9months (mostly @ 35psi)
Carbon block and sediment age: 1-2 months

 

[Woodyman]

What kind of DI are you using. I noticed you said you packed it yourself, but what style/brand?

Also just a single stage of DI it appears?

 

[Woodyman]

Also just to throw this out for you as well, testing ultra pure (RODI) water often results in testing errors.

On top of that, that Hanna meter is setup specifically for testing in saltwater. So freshwater will skew the results as well.

Have you ever done any ICP analysis of your RO/DI?

 

[Woodyman]

If phosphate is bleeding through in a measurable amount adding a second stage of DI would help remove it. For that I'd recommend a specialty cartridge from spectrapure.

SpectraPure - Innovators in Water Technology

SpectraPure, Inc. is an Industry Standard in the Water Purification world. From Drinking Water to Aquarium Systems, you don't just want pure water, you want the PUREST Water! Get it with SpectraPure!

spectrapure.com

That's the one I'd go with.

 

[Woodyman]

I believe I've seen something from @Randy Holmes-Farley about phosphate in RO/DI in the past but I may be mistaken. It's been a few years.

 

[aloonj]

What kind of DI are you using. I noticed you said you packed it yourself, but what style/brand?

Also just a single stage of DI it appears?

Prior to last week was Reef Zlements Aqua pure, now its https://www.osmotics.co.uk/1-litre-colour-changing-di-resin.html

And yes, single of DI currently.

Also just to throw this out for you as well, testing ultra pure (RODI) water often results in testing errors.

On top of that, that Hanna meter is setup specifically for testing in saltwater. So freshwater will skew the results as well.

Have you ever done any ICP analysis of your RO/DI?

ICP was quite a few months ago, so time to do a new one!

 

[Woodyman]

Prior to last week was Reef Zlements Aqua pure, now its https://www.osmotics.co.uk/1-litre-colour-changing-di-resin.html

And yes, single of DI currently.



ICP was quite a few months ago, so time to do a new one!

What did your ICP last register for phosphate?

 

[AJsReef]

Additional DI stage is the correct solve. I live FL where we have high phosphate and silicates in our water source. 2 DI resin stages is a minimum for my water source. I now run a 3 stage DI (Cation/Anion/Mix Bed) and a Spectrapure silica buster at the end. The Spectrapure is overkill but its ensures that my product water is free of silica and phosphate.

 

[vetteguy53081]

This time of the year, many municipalities add phosphate, flouride and other compounds to the water at high concentrations which may be your source

 

[aloonj]

Thanks all. Second stage DI coming soon!

 

[Randy Holmes-Farley Verified Community Expert]

I have an entirely different opinion: ignore the trivially small input from the RO/DI. Just ensure it is 0 ppm TDS and you are good to go. Foods (or contaminated rock) are the cause of elevated phosphate.

Aquarium Chemistry: Phosphate And Math: Yes You Need To Understand Both

Foods are by far the most important source of phosphate in most aquariums. In considering whether sources of phosphate other than foods are important, one must carefully look to the actual amounts involved to determine whether other sources are even worth trying to minimize.

reefs.com

Comparison of Food Sources of Phosphate to Other Sources
What about other sources of phosphate, like the “crappy” RO/DI water containing 0.05 ppm phosphate? A similar analysis will show it equally unimportant relative to foods.

Let’s assume that the aquarist in question adds 1% of the total tank volume each day with RO/DI to replace evaporation. Simple math shows that the 0.05 ppm in the RO/DI becomes 0.0005 ppm added each day to the phosphate concentration in the aquarium. That dilution step is critical, taking a scary number like 0.05 ppm down to an almost meaningless 0.0005 ppm daily addition. Since that 0.0005 ppm is 40-600 times lower than the amount added each day in foods (Table 4), it does not seem worthy of the angst many aquarists put on such measurements. That said, tap water could have as much as 5 ppm phosphate, and that value could then become a dominating source of phosphate and would be quite problematic. Purifying tap water is important for this and many other reasons.

 

[merkmerk73]

If phosphate is bleeding through in a measurable amount adding a second stage of DI would help remove it. For that I'd recommend a specialty cartridge from spectrapure.

SpectraPure - Innovators in Water Technology

SpectraPure, Inc. is an Industry Standard in the Water Purification world. From Drinking Water to Aquarium Systems, you don't just want pure water, you want the PUREST Water! Get it with SpectraPure!

spectrapure.com

That's the one I'd go with.

I’m going to try this

Got a 2 stage DI kit

Will replace all filters and then do this and see how the phosphate is after

I know Randy says it’s not necessary but I’d rather dilute my phosphates where I can