View Full Version : RO/DI water has high ph (9.9). What to do?
tonypittman
02-11-2007, 11:26 PM
I recently added a CA reactor, in search of a way to stabilize and maintain ph.
I then happened to use my new ph probe on my topoff water (RO/DI) and was surprised to see that it registered a ph of 9.9.
I had always tested ph of prepared saltwater that was going in during water changes, but now realize that I need to deal with the pure topoff water.
The question is...what should I do to lower the ph of this water before it goes in as topoff water? Any suggestions?
Also, is my RO water ph so high because of my local water supply? I thought it was supposed to be somewhere around 7.0 coming right out of the RO unit. I changed all of the filter cannisters just a couple of months ago.
CarmieJo
02-11-2007, 11:34 PM
Have you tested the pH of your tap water?
Seahorsedreams
02-12-2007, 12:57 AM
Typically RO/DI product water is around 7.0. But with very pure water there can be a lot of inaccuracies with readings.
Pure water also doesn't have a very "developed" buffering capacity so it can be very variable depending on outside influences.
A high pH of RO/DI water mixed with a solid 8.2 SW mix will not bring the new pH to an average between the two. The buffering capacity of the SW will lower the pH of the RO/DI significantly.
There is also a reaction/conversion of ammonia and cloramines of the tap water pretreatment that can result in a higher pH... I forget the exact mechanism at the moment.
What is the pH of your display tank? That would be the most valuable piece of information. If it is normal than let everything be. If you start messing with chemistry based on the possible inaccruate pH reading you will throw everything out of whack and it is hard to recover from that.
There is talk of the resulting pH from a SW mix will be increased in the future to a minimum of 8.4. We keep the pH of our tanks on the hairy edge of low for the most part.
It's not something I would worry about or alter unless there is problems with your reading in your display.
tonypittman
02-12-2007, 01:30 AM
OK..thanks. The display is currently at 8.5, but I've increased the CA reactor output, trying to get it to 8.2-8.3.
I was wondering whether or not the high ph RO/DI water was causing the tank to creap higher. Seems unlikely, given the responses.
Seahorsedreams
02-12-2007, 01:39 AM
No, I can't discredit that it is driving your pH up. But I wouldn't be concerned with a nighttime pH of 8.5.
tonypittman
02-12-2007, 01:51 AM
Gotcha. I just tried flushing the membrane (something I need to do more often...haven't done it in months). That got the RO output down to do around 8.9. I think I'll leave it as is for now and see how the display goes.
Seahorsedreams
02-12-2007, 02:09 AM
*blush*
I've never flushed the membrane.
tonypittman
02-12-2007, 10:47 AM
You may want to try it...looks like it made a difference for me. The manual actually says to do it every month for 15 minutes.
Seahorsedreams
02-12-2007, 11:26 AM
I really know I should. It's pure laziness that I haven't.
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