Phosphate in RODI water

[TheKyle]

I’ve been battling with phospates and was shocked today when I tested my freshly mixed saltwater and found 0.034 phosphates using Hanna checker. I’m worried about the phosphates I’m adding to my system with rodi water every time my ato tops off the tank.

My rodi system consists of two sediment filters followed by two carbon blocks, then older first stage to membrane, newer second stage Ro membrane (water saver upgrade) then two separate di resin canisters. I measure about 8-9 tds before di resin and 0 tds after di resin. I have as much pressure as I want available and set my regulator for the system at 85psi.

So which component of the system is responsible for removing phosphate? I see some people recommend changing carbon blocks, but if carbon can’t remove phosphates in the aquarium, why would it help in my rodi system? Do I need to replace my older RO membrane? Di resin? I appreciate any advice.

 

[Scrubber_steve]

I’ve been battling with phospates and was shocked today when I tested my freshly mixed saltwater and found 0.034 phosphates using Hanna checker. I’m worried about the phosphates I’m adding to my system with rodi water every time my ato tops off the tank.

I'm thinking that PO4 level is normal for an aquarium, isn't a problem unless you're having high PO4 reading from your tank, &, it could be from the salt you're using, not your RODI water?

 

[TheKyle]

I'm thinking that PO4 level is normal for an aquarium, isn't a problem unless you're having high PO4 reading from your tank, &, it could be from the salt you're using, not your RODI water?

I agree as a tank reading that would not be bad, but my tank was at 0.15 ppm phospate before today’s massive water change. So I’m not really worried about the levels for water changes because I’m removing a ton of phosphate in the process. What concerns me is that my top off water is constantly adding phosphates without removing any.

 

[TheKyle]

I will have to test my rodi water without salt to rule out the salt mix. Didn’t think of that before

 

[Scrubber_steve]

I agree as a tank reading that would not be bad, but my tank was at 0.15 ppm phospate before today’s massive water change. So I’m not really worried about the levels for water changes because I’m removing a ton of phosphate in the process. What concerns me is that my top off water is constantly adding phosphates without removing any.

as I said, it could be your salt? Get fresh water PO4 test to check your RODI water to see if it is the source.

 

[Randy Holmes-Farley]

I’ve been battling with phospates and was shocked today when I tested my freshly mixed saltwater and found 0.034 phosphates using Hanna checker. I’m worried about the phosphates I’m adding to my system with rodi water every time my ato tops off the tank.

My rodi system consists of two sediment filters followed by two carbon blocks, then older first stage to membrane, newer second stage Ro membrane (water saver upgrade) then two separate di resin canisters. I measure about 8-9 tds before di resin and 0 tds after di resin. I have as much pressure as I want available and set my regulator for the system at 85psi.

So which component of the system is responsible for removing phosphate? I see some people recommend changing carbon blocks, but if carbon can’t remove phosphates in the aquarium, why would it help in my rodi system? Do I need to replace my older RO membrane? Di resin? I appreciate any advice.

that level is insignificant to the tank balance of phosphate. You add a hundred times as much every day in foods as using that water for top off will add.

 

[Randy Holmes-Farley]

I show the data supporting my assertion that it is insignificant here:

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.

www.advancedaquarist.com

 

[Randy Holmes-Farley]

From it:


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.

 

[Dvanlier05]

I heard on Melev's Reef livestream that you cannot test for phosphates in RODI water because there are no ions in the water, or something like that. He said it will give you a false reading.

 

[TheKyle]

that level is insignificant to the tank balance of phosphate. You add a hundred times as much every day in foods as using that water for top off will add.

Thanks for putting this into perspective for me. Makes a lot of sense now. I feel silly now for not running the numbers myself.

Another win for the scientific approach!

 

[badams.one]

From it:


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.

Hey Randy, I came across this post and wanted to follow up with a question on the topic. The point made on the top off is valid, but what about the PHO in the RO water if one is doing a water change with say, 35-40 gallons, which would be 25/30% of the total water volume in the system. Clearly there would be more concern in this scenario.

What is the best way to test Phosphates in RODI if it can even be done?

 

[badams.one]

From it:


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.

Hey Randy, I came across this post and wanted to follow up with a question on the topic. The point made on the top off is valid, but what about the PHO in the RO water if one is doing a water change with say, 35-40 gallons, which would be 25/30% of the total water volume in the system. Clearly there would be more concern in this scenario.

What is the best way to test Phosphates in RODI if it can even be done?