Phosphate

Randy Holmes-Farley

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I took a gallon of my RODI water mixed with salt and tested it. The level in my fresh saltwater was .26, where my tank is at .07 and rising. Unless the phosphates were coming from the salt, which I don't think is possible, but I may be wrong. I guess it might not be the main source, but it is definitely a source.

Mike

Definitely not the main source when used as top off, and possibly not even worthy of thinking about, but a new DI or a second DI will lower it.

I'd equate it to worrying about heat loss from drafts around an old window, when the window next to it is actually open. :)
 
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am3gross

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Definitely not the main source when used as top off, and possibly not even worthy of thinking about, but a new DI or a second DI will lower it.

I'd equate it to worrying about heat loss from drafts around an old window, when the window next to it is actually open. :)

If this is the case then I am extremely confused, Phosphates have to come from somewhere. Over the last month the only thing that has changed in my system has been me doing water changes. ( ICP results showed tin in my system) Over the last month I have watched the phosphates slowly climb. My assumption was the RODI filters as they were slowly losing effectiveness.

All my water parameters have stayed the same, with the exception of the phosphates. As the phosphates rise, so does the amount of Cyano in the tank. Before the water changes there was no nuisance algae of any sort. I get the food is a major contributing factor, but IF the same amount of food is being used, ( 2 cubes frozen, 2x PE Pellets) and there has been no algae before then why the change now?
 

Randy Holmes-Farley

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If this is the case then I am extremely confused, Phosphates have to come from somewhere. Over the last month the only thing that has changed in my system has been me doing water changes. ( ICP results showed tin in my system) Over the last month I have watched the phosphates slowly climb. My assumption was the RODI filters as they were slowly losing effectiveness.

All my water parameters have stayed the same, with the exception of the phosphates. As the phosphates rise, so does the amount of Cyano in the tank. Before the water changes there was no nuisance algae of any sort. I get the food is a major contributing factor, but IF the same amount of food is being used, ( 2 cubes frozen, 2x PE Pellets) and there has been no algae before then why the change now?

There's no reason to not ensure the TDS is 0 ppm from the RO/DI, and to even add a second DI in series if you want. Phosphate is one of the easier ions to evade an RO/DI.

Certainly, lots of water changes with that water are going to increase phosphate, not decrease it. As an aside, even with 0 ppm phosphate in the water, water changes are typically not super effective at reducing phosphate for the reasons described below.

But even with no sources other than foods, phosphate often rises, and can do so long after the tank is set up and functioning stably.

One reason is that calcium carbonate rock and sand can be a major sink for phosphate as it binds to the bare surfaces. Eventually those will come to equilibrium with the phosphate level in the water. Think of that like the surfaces becoming saturated.

After that point, any excess phosphate from any source will raise the level in the water.

In any case, my point is not that source water cannot be a source of phosphate. Often it is, and if raw tap water is used it can be huge. My point is that it is that 0 ppm TDS RO/DI is very rarely the main source (if ever), and trying to solve a phosphate problem by dealing with a minor contributor is not typically the best answer.
 

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