RO/DI pH

[S!mon]

my meter is saying that the pH of my RO/DI is 9.8...can this be right. The meter was just calibrated less than a week ago. Thanks.

 

[ihopss]

I would check it again, that seems high for even tap Water, about six is where mine ruins, that is without salt added.

 

[ufotofu]

9.8?! I've never seen tapwater that high...better double check that with another test kit or at least clean your vials and test again. If you're using electrodes better recalibrate with at least a two point cal (7.0 and 10.0)and test again. If it's still off, clean the electrode using electrode cleaning sol'n, make sure there are no bubbles in the electrode and that salts haven't corroded the connections/internals and refresh the calibration.

Totally pure water should be pH neutral, or 7.0. I've found most test kits to be off a little, but shouldn't be off by more than 0.1 or 0.2 units (electrodes should be much closer if cal'ed properly). Remember, the pH scale is logarithmic (a small difference in pH means a big diff in [H+]. So, make sure your vials are clean and your reagents are not fouled. If you have a TDS meter on your RO/DI unit it should read as close to 0 as possible - no more than a very few ppm on the output water. You may need to replace your media if it's reading high. Don't have one? You can pick up a handheld unit at most decent LFS or online for about 50-75 bucks.

 

[S!mon]

My TDS is 0. I think this is why a pH reading cannot be trusted with RO/DI water. I am asking this because all of my mixed water has a pH of 7.8-7.9 with airation. I've been using Kent salt but I just bought some Coralife today and the pH is the same 7.8-7.9.

 

[ihopss]

your first post was 9.8 was that a mistake

 

[S!mon]

Thats the pH of my RO/DI before any salt is added.

 

[Anonymous]

This issue comes up from time to time. There is no point in measuring the pH of ultrapure water due to the lack of ion/salt. In very low ion water, the pH meter will go haywired.

Just forget about it and measure the pH *after* the salt is added and see if the reading is too high or too low.

 

[S!mon]

My mixed water has a pH of 7.82 with two diffrent salts. I took a batch outside to mix and the pH went up to 8.2, so I'm going to run the air supply for skimmer outside and hope this solves the problem. Thanks everyone.

 

[Old Man Of The Sea]

That`s really too high as others said it is. After my RO/DI unit makes my tanks water, the water before the salt is added, the Ph I figure is somewhere around 5

 

[Anonymous]

pH is a measure of H+ ions in solution. Pure water (distilled water, for instance) has an equal number of H+ and OH- ions and is considered neutral. It should have a pH of 7.0. Since DI water is deionized it lacks some or all of these ions and measuring its pH is futile. Thus, DI water will typically not read a pH of 7.0. I have seen it read anywhere from 3 to 10 with a meter.

 

[Anonymous]

This issue comes up from time to time. There is no point in measuring the pH of ultrapure water due to the lack of ion/salt. In very low ion water, the pH meter will go haywired.

Just forget about it and measure the pH *after* the salt is added and see if the reading is too high or too low.

Or what ck said.