# Can phosphate affect pH?



## smithgrind_who

I was talking with a few people I know about fresh water fish aquariums, and I there was a topic about phosphate. I'm curious to know if phosphates can affect pH levels? I know it can lead to algae problems, but can phosphates be a cause for low pH levels?


----------



## Dr. Giggles

Usually with high phosphates a drop in ph will occur because high nitrates and phosphates go hand in hand.


----------



## elTwitcho

I'm not sure in which direction it would go, but phosphates will certainly affect ph. Those ph adjusting chemicals contain high levels of phosphates, so I'd imagine there's a correlation


----------



## smithgrind_who

Thanks for the replies! I wasn't really sure if phosphates could affect the pH. Does any know the chemical equation? I am curious to know what the process is doing as to the pH dropping or rising.


----------



## Dr. Giggles

I would like to add, that if you have a high KH it is very possible that high phosphates probably will not affect PH. Only create green water effect. I wasn't thinking clear yesterday.


----------



## FrankP

The way phosphate presents itself in water is dependent of ph.
In freshwater tanks (ph is 6.5-7.5) most phosphate is in the form H2PO4- wich in fact is a base and will bound with pos. ions like Ca+ for example.

So the way phosphate will influence the ph is dependent of the ph itself wich is dependent of a number of things like CO2 , peat, plants, minerals etc.

If phosphate is in the form HPO4 2- (the 2 must be in the right corner ofcourse), then it is slightly acidic.
But the overall effect on neutral conditions is very little, unless you put enormous amounts of phosphates into the water.

Hope this will clear things a bit.


----------



## elTwitcho

Damn Frank, thanks for that little nugget of wisdom, I didn't know that.


----------



## smithgrind_who

FrankP said:


> The way phosphate presents itself in water is dependent of ph.
> In freshwater tanks (ph is 6.5-7.5) most phosphate is in the form H2PO4- wich in fact is a base and will bound with pos. ions like Ca+ for example.
> 
> So the way phosphate will influence the ph is dependent of the ph itself wich is dependent of a number of things like CO2 , peat, plants, minerals etc.
> 
> If phosphate is in the form HPO4 2- (the 2 must be in the right corner ofcourse), then it is slightly acidic.
> But the overall effect on neutral conditions is very little, unless you put enormous amounts of phosphates into the water.
> 
> Hope this will clear things a bit.
> 
> 
> 
> 
> 
> 
> 
> 
> [snapback]1061856[/snapback]​


Thanks for the explanation FrankP! I just got a phosphate (PO4 3-) test kit and my tap water has a reading slightly higher than 0.5ppm. It's frustrating to know if it's dihydrogen phosphate ion or monohydrongen phosphate ion. I know the nitrification process will increase the tank water to acidic levels, but how does one determine what the phosphates are doing to the water's chemistry?


----------



## FrankP

SW,

First of all, your phosphate level is ok, nothing to worry about.

Second I ve digged in my old chemistry books and its a very long time since i used them so I keep it to the basics.
To answer your question correctly there are many chemical processes needed to explain but I can do this very simply:

Phosphate (PO4) is actually a salt derived from the weak acid H3PO4, this negative ion (PO4_) will bond with pos. ions and this process will not influence the PH!
That is basicly the answer to your question.
And how to determin this phosphate concentration will interact with the pos. ions is dependent of the Ph.
The key elements that determin the Ph are CO2 , CO3-hardness, use of peat and oxydation.
So I think it is more relevant to determin those elements to analyze your water chemistry instead of the Phosphate-level wich only increase the algue-grow if high level (PO4) is determined.
Hope this will do!


----------

