RODI water has phosphates

[brrdawg]

So my tank is a little over a year old and the first 6 months everything was going great and having a lot of fun. I got a booster for my RODI unit and it’s been crap since. Phoshates have always been over .1 since that time. I finally took the booster off and just went with straight RODI. So I got new filters and a new RO cartridge replacement as well as new DI resin. So I tested the water that was going to be a water change and the phosphates were .05 on a Hanna checker and I also tested with Red Sea at .04. Is this normal? I have always had my TDS say 0. I got hair algae and large cell Amphidinium which both started around this time. Just wondering what to do. It’s been a tough and expensive problem to have. Current phos is around .08 in the tank. But has been about .16 for months. Nitrates between 8-10. Also have been running GFO for months to try and get phos down.

 

[KrisReef]

Maybe you should get a new TDS meter, and make certain the resin cartridge is full so the water can’t get by without filtering?

 

[brrdawg]

Yeah I may look into a new tds meter. It appears to be working but who knows I guess. Thank you for the reply.

 

[Randy Holmes-Farley]

There's zero concern with 0.04 ppm phosphate in RO/DI water. . Zero phosphate in RO/DI water is one of the inappropriate fixations of the hobby. It is an trivially small contribution to phosphate in the tank.

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.

The same sort of calculation applies to analyzing other phosphate issues, such as the GAC in scenario three. The issue of finding “high” phosphate in GAC soaked in fresh water was frequently quoted as a reason to use one or the other brand of GAC, and probably still is. But simple analysis as shown above for the food rinsing puts the lie to this being a big problem.

 

[Tamberav]

The TDS meter is probably working correctly. They have a range of error and are hobby grade like most everything else. The fact it reads zero does not surprise me.

 

[Randy Holmes-Farley]

The TDS meter is probably working correctly. They have a range of error and are hobby grade like most everything else. The fact it reads zero does not surprise me.

If there is 0.05 ppm phosphate, and say, 0.05 ppm of sodium as counterions, and little else, it should read 0 ppm.

 

[brrdawg]

Ok thank you everyone for their help. I really appreciate it. I feel like when I have done water changes things tend to get worse in the tank so I may just chill out on changes for a bit. My phos went up from .07 to .09 after a change.

 

[Randy Holmes-Farley]

Ok thank you everyone for their help. I really appreciate it. I feel like when I have done water changes things tend to get worse in the tank so I may just chill out on changes for a bit. My phos went up from .07 to .09 after a change.

Those values are all fine, and the water change did not boost it. That difference would be test error, unless the RO/DI was far higher than you reported.

 

[PedroYoung]

So I'm having the same problem that's not a problem haha. One question I have is should RODI systems remove PO4 to zero if working properly (I understand that it's almost meaningless as a source of PO4). Chemically should the DI resins remove PO4? I'm on a well and have a pretty aggressive DI setup with separate Anion and Cation beds, a mixed bed with BRS "pro" mixed resin and 2 standard mixed beds and still have .05-.1 ppm. I'm having a hard time squaring hair algae and cyano issues in a 3 yr old reef with just feeding.

Untitled by Peter Young, on Flickr

 

[PedroYoung]

@Randy Holmes-Farley , do you have any insight into my question above regarding removal of PO4 through RODI train? Which "stage" should be doing the phosphate removal? RO? DI?

 

[Randy Holmes-Farley]

@Randy Holmes-Farley , do you have any insight into my question above regarding removal of PO4 through RODI train? Which "stage" should be doing the phosphate removal? RO? DI?

Both. An ro will reject most of it, and a di of sufficient capacity can remove all of it, but hobby di designs may still leave some.