Do chloramines and PH raising chemicals pass through RO membranes? - The Planted Tank Forum
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post #1 of 4 (permalink) Old 02-07-2016, 06:26 PM Thread Starter
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Do chloramines and PH raising chemicals pass through RO membranes?

I use RO water and have noticed that the PH of new water with a TDS of less than 10 and a KH of less than 1 has a PH that is still around 8.0 . It is still buffered by something very strong because it does not easily change by adding acid buffer or neutral regulator. I don't normally add those to my water but I was playing around the other day and found it curious. I used both a PH pen and standard and high range test kits to confirm the high PH.

Wondering if the chemicals they add to make the water non corrosive passes through the membrane also got me wondering if chloramines pass through. I normally just re-mineralise with Equilibrium and use an airstone for a day before adding to the tank but now I wonder if I should be treating for chloramines. I change 50% a week and have had no issues but I am curious.
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post #2 of 4 (permalink) Old 02-08-2016, 03:25 PM
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My tap water PH is in the mid 8's or higher but is close to 6 after the RO. I've read posts from others that still have high PH after the RO. I don't know if it depends on the amount of carbon filtration if any that removes whatever is causing the high PH or not. My unit has a carbon block filter after the sediment pre-filter and then an activated carbon final filter after the membrane. Here is some information on chloramines.
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post #3 of 4 (permalink) Old 02-08-2016, 03:56 PM
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When most of everything is removed from the water via RO there is very little remaining to dictate the pH.
A little trace of anything can make quite a difference in the pH. A TDS under 10 (but not closer to zero) suggests something is still getting through, or perhaps there is something in the collection barrel.

If you leave this water out, especially if you circulate it, does the pH drop? The RO water can pick up CO2 from the air and this will lower the pH.

If you add something that will lower the pH (perhaps some peat moss) does that lower the pH?

What other tests do you have? (GH, KH, other?)

Do you know what the water company adds to keep the pH up? (Call them and ask) Then look that up to see it it is removed via your RO unit. Most things are, but yes, there are a few things that can make it through the membrane. For this reason other filters are often used either before or after the RO unit.
Check with the manufacturer, perhaps there is something you can add to your system. If it is something simple, perhaps you could add a HOB filter on your collection barrel and just run activated carbon or something in that overnight.
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post #4 of 4 (permalink) Old 02-08-2016, 11:05 PM Thread Starter
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I guess it is something getting through the membrane. I will have to check with the water company to know for sure what it is. In the past it has never been an issue and even now I never worry about PH, the fish are all adjusted to it. Merely curious and wondered about chloramines. Water companies have almost all gone to high PH to prevent corrosion so we all will deal with it eventually.

And no, no amount of peat has any effect. GH is about 7 and KH of tap is about 15, TDS is around 120. PH is 8.2
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