High pH RO water normal?

[nacra99]

Hi!

Lately, my RO unit has been making RO with a pH of 9+ (Previously i have been getting about pH 6+). The first thing i did was to change all the pre filters and membrane and found that it was still making pH 9+. My TDS is approx 3-8 so i know the membrane is fine. I tested the water out of the tap and found that the pH also increased from 7.8 to 9-ish. The city must have added soemthing to the water.

Is this high pH normal for RO water? With this sudden increase in pH, i'm finding it really difficult to lower my pH to 5.5-6 with peat for my macrostomas. This was previously not a problem.

Could it be that the RO is not removing the additive form the tapwater? (are RO membranes even capable of doing that??) I've always had the impression that RO water is usually has a lower pH that feedwater... is this not correct?

Cheers
Marc

[Alight]

CO2 levels can make a very large difference in the pH of RO water.

This may be why pH is lower in RO than the feed water, in many cases. The CO2 will go through the membrane, but the rest of the buffers (calcium carbonate, etc. ) won't so the pH will be lower. If the RO water is aerated for a while, it will tend to go higher.

It doesn't take much carbonate to change the pH of RO water, and that may be waht is happening to your RO water now. However, it also takes very little acid to lower the pH of RO water drastically as well.

I'm a bit surprised that peat is not lowering it. Are you adding some tap water to the RO as a mix? This would make it difficult to lower, but you must be adding something to bring the water GH up a bit, right?

[pwsusi]

I don't have the answer to your question as to why pH is so high coming out of the R/O unit but I can say that my well water out of the tap is in the 7.8-8.2 range and after R/O and sitting for 24hrs it only drops to 7.4-7.6. I don't use peat to lower the pH, I use muriatic acid which is very cheap (I get it for about $5 at Lowes). A little goes a long way - I have 3 55 gallon drums tied together and I put just enough to cover the bottom of a 1 cup measuring cup and that is usually enough to lower it into the mid to low 6's.

[kaceyo]

Even if the product water is higher in pH I'd think it would be easy to bring back down. Have you tried calling the water co in your area? My tap water is very soft, around 44ppm TDS and KH between 1 and 2 degrees, but the pH is near 8, which is unusual for such soft water. I think they add something to the water to keep it from becoming acidic. I'd guess they did start doing something different at the source so calling the city would be the only way to find out what changed. Then you can figure out what to do about it. Just a suggestion.

Kacey

[nacra99]

Thanks for the insight.
I read that strong acids (in the chemistry sense) are difficult to handle and so i'm shying away from it... for now....

My peat is lowering the pH, but not as much as before. Previously with an RO water of pH 6.5 (reconstituted to KH 2, GH 4-6 to avoid sudden crashes) , after 24 hrs of peat filtration, i get a pH of about 5.5 - 6. But now when i start off with RO pH of 9+, i can only get down to 7.0 or so, so there's probably something in the water buffering it at 7 (perhaps it's the KH of 2?)

For now i'm resorting to adding Sechem's Acid Buffer to keep the pH down.

[pwsusi]

What is the conductivity of the water after you mix your tap water back in? Maybe it is too hard and the pH of the water is bouncing back up. With a KH of 2 I wouldn't think that would be the case.
When I mix down to 100-150 micro siemens the pH of the water seems to stay wherever i put it.

[kaceyo]

With the KH at 2 you should be able to lower the pH pretty easily. Did you change the way you're remineralizing the RO water? Do you know what the KH was before the pH changed? Though I can't imagine the KH is the problem at 2dKH.

Kacey

[nacra99]

My TDS is about 90- 100 mS after reconstitution. Little fluctuation due to the difference in each scoop of RO right.

Kacey, KH out of the tap is about 5-6. I just realized that it was exactly the same as before.. the KH out of the tap remains the same... but the pH is different. Very Puzzling..... perhaps it's the city's new spring/summer water formula....??

[kaceyo]

Interesting. I called my city water co when I started with discus and they sent a rundown of all the water sources and treatment plants with parameters of the tap water from each. They must have started addng something. Is it possible your tests (probe/reagents) are off?

[Alight]

With pH that high, and kH that low, it's probably magnesium carbonate. It will buffer to a higher pH than calcium carbonate.

It's probably why your final pH is settling higher with your kH at 2 than it should according to the calcium carbonate scales.

Are you reconstituting with tap water, or with minerals and bicarbonate. If with tap water, that would explain your difficulty in using peat. It's harder to explain if you're using chemicals to reconstitute as there will only be a miniscule amount of magnesium carbonate left in your RO water. So little that I'd be surprised if there would be any difference after the peat treatment.

[raglanroad]

Try new peat. If you are using granules, the effect is not so strong as with Home Depot peat.

[nacra99]

I use the canadian peat from home depot.

I have since given up on peat and the peat has since been relegated to my Orchid pots. I now use a mixture of Sechem's acid and alkaline non phosphate buffers. It doesn't buffer as well as phophate buffers, but the day/night pH fluctuations are not bad enough to bother the fish.

[kaceyo]

Hi Marc,
Did you ever find out why your pH is so high now?

[nacra99]

Hey Kacey,
I tried calling my water company but was put on hold and finally dropped.... *sigh* New Orleans is certainly not the same.......
Actually, i would't be surprised if something was added to the water. A new FEMA trailer park just sprang up down the street from where i live... probably some contamination from all the re-routing of all the water to the trailers.

[kaceyo]

I'm sure it's changed quite a bit, but they still have redial don't they? ;) Actually your set up better than most to deal with the water issues in your area. I'm not sure how accurate the info you'd get from them would be with things as they are. Are discus people in your area that use tap (w/out RO etc.) having probs with their water quality and stability?

Kacey