Phosphate in my RODI Water?!

[Randy Holmes-Farley]

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?

The source water is not the main source of phosphate for that tank, but is a substantial source. Foods are a bigger source.

Lowering the phosphate will take effort, even if you cut off the Ro/DI source, but keep in mind that algae will grow equally well at 0.2 ppm and 1.7 ppm phosphate. More and more of any needed nutrient does not necessarily make algae grow faster and faster, because something else becomes limiting (in this case it may weell be a source of nitrogen (N).

 

[Tom Davey]

All, I have a the same issue, I change all my RO/DI filters regularly . I recently had an ICP test done to verify my readings and my RO/DI had PO4 within a week of replacing all filters on my RO/DI system. I do not think the built in TDS meter is an issue the source water must have a fairly high level of PO4. My Question is how to filter it out?

 

[Randy Holmes-Farley]

All, I have a the same issue, I change all my RO/DI filters regularly . I recently had an ICP test done to verify my readings and my RO/DI had PO4 within a week of replacing all filters on my RO/DI system. I do not think the built in TDS meter is an issue the source water must have a fairly high level of PO4. My Question is how to filter it out?

What level? It may be insignificant even if well above the tank water level (which is what?).

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.

 

[Tom Davey]

What level? It may be insignificant even if well above the tank water level (which is what?).

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.

Phosphorus 17.64 ug/l
Phosphate 0.05 mg/l

 

[Randy Holmes-Farley]

Phosphorus 17.64 ug/l
Phosphate 0.05 mg/l

If that is in tank, it is perfect, IMO.

If that is in the ro/di, it is an insignificant contributor and I do not recommend doing anything to lower it.

 

[Tom Davey]

If that is in tank, it is perfect, IMO.

If that is in the ro/di, it is an insignificant contributor and I do not recommend doing anything to lower it.

Thats the RD/DI water the tank is below

151.9 µg/l
0.47 mg/l

 

[Randy Holmes-Farley]

Thats the RD/DI water the tank is below

151.9 µg/l
0.47 mg/l

I'd ignore the RO/DI as dropping it to zero will not have a noticeable effect on the reef tank values.

If you want to lower the phosphate in the tnak, you likely need to export mnore, such as by growing macroalgae or using GFO. Whether lowering the tank level will have an observable effect on organisms is not really clear, IMO.

 

[Necrodaemus]

Resurrecting this thread. I tested my RODI water for phosphates with a Hanna Phosphorus ULR this morning and 2 tests register 8ppb and 5ppb (margin of error between the 2, sure). My RODI shows 0 TDS using a handheld TDS meter. I know PO4 won’t show on a TDS reading but is it still possible to have phosphates in my RODI? I run a 4 stage with mixed bed resin. Carbon, sediment and membrane all changed around 4 months ago and resin is only 1/4th depleted. Possibly silicates throwing the PO4 test off?

 

[Randy Holmes-Farley]

Resurrecting this thread. I tested my RODI water for phosphates with a Hanna Phosphorus ULR this morning and 2 tests register 8ppb and 5ppb (margin of error between the 2, sure). My RODI shows 0 TDS using a handheld TDS meter. I know PO4 won’t show on a TDS reading but is it still possible to have phosphates in my RODI? I run a 4 stage with mixed bed resin. Carbon, sediment and membrane all changed around 4 months ago and resin is only 1/4th depleted. Possibly silicates throwing the PO4 test off?

Those phosphate values are very low and are an insignificant contributor to the net phosphate balance in your reef tank.

Yes, they can certainly be accurate.

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.

 

[Necrodaemus]

Those phosphate values are very low and are an insignificant contributor to the net phosphate balance in your reef tank.

Yes, they can certainly be accurate.

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.

Thank you, Randy!

 

[Randy Holmes-Farley]

Thank you, Randy!

You're welcome.

Happy Reefing.