Phospate level in RO water

[jonray]

Hi all.

I currently have phosphate levels of 0.08 measured by the Hanna ultra low phosphorous checker. I was a little dismayed to find that my ATO RO reservoir water had phosphate levels of 0.0245. I have recently changed my RO unit filters and TDS is 0.

I only have a small tank and a large ATO reservoir so the reservoir water can be in there for 4 weeks before it is used. The reservoir is in a sunny room so the question is would phosphates increased naturally over time in the reservoir? The water is left to stand and is not aerated.

Thanks in advance

 

[mcgyvr]

Put some fresh RO water into a clean glass.. Check it for phosphate level..
report back..

Is the ATO container sealed?
Could be phosphates leaching from the plastic of the ATO container I guess..

 

[jonray]

Will do a fresh batch at the weekend. The container is not sealed and the container is plastic.

 

[bertoni]

That level is close to the error limit for the device, and there might be a bit of organic debris or other contamination in the container. I might try wiping the reservoir down with a bit of vinegar. I agree that testing some water straight from the filter might help pin down any possible source of phosphate.

 

[outssider]

according to hanna, they list the 736 as a "marine" phosphorus meter. I have been using this checker for many years but I'm not too sure that it's accurate in fresh water. When I've tested fresh water (from the tap and my ro'di reservoir) it seems accurate but I wouldn't make a bet on that. Maybe call hanna and ask them if it's accurate in fresh water.

 

[jason2459]

Hanna has stated in a reply to a question I sent to them that the 736 is not accurate for freshwater.

 

[bertoni]

Oops, I agree that the HI 736 is rated only for saltwater. I missed that.

 

[jonray]

Wow. Thanks for the help guys. I would have wasted a lot of time and cash chasing something that possibly doesn't exist. Large water change time methinks.

 

[Dan_P]

Hanna has stated in a reply to a question I sent to them that the 736 is not accurate for freshwater.

Does that mean underestimates the amounts? If so, phosphates in freshwater would be much higher than indicated by Hanna.

The test chemistry is sensitive to pH. Without the buffering of seawater, the test solution acidity in freshwater is possibly too low for the color development. So, that means no detection or underestimation of phosphates.