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Posted by CheezWiz on April 19, 2005, 9:01 pm
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I use this:
http://www.kentmarine.com/saltwater/opm.html
CW
>I have a 35 gpd Ro unit (with carbon and sediment filters, no DI filter).
>I've been reading up on RO this evening and found several references that
>say that RO water can be more acidic than tap water (lower pH) because RO
>membranes do not reject CO2. This concerned me since I've been having
>water quality problems for some time and thought that it might be a problem
>with my sea water not having enough calcium. I bought a Nutrafin pH test
>kit and a Nutrafin Calcium test kit. I got some interesting results. For
>the tap water, I got a pH of 7.5 with 60 mg/L of calcium. At present, the
>water in my marine tank has a pH of 7.5 (yes, I know it is too low) with
>calcium at 280 mg/L. The RO water has a pH of 5.0! Calcium was
>essentially 0. I don't know if it is normal for the pH to be so low in RO
>water, but I suspect that adding this water unbuffered to my aquarium is
>the root cause of my problems (thankfully, I have quite a lot of sea sand
>in the tank, so it does prevent a pH crash below 7.5.). I understand that
>RO units do not always result in a substantial drop in pH since it depends
>on the amount of dissolved CO2 gas that is present in the feed water.
>Apparently, my tap water has a high CO2 content.
>
> This is a good argument for strict testing of make up water, especially
> since, in my case, I never tested the pH of the RO water, assuming that it
> was neutral (which it is obviously not). I plan to start adding sodium
> bicarbonate and calcium chloride to the RO make up water in the future,
> and aerating the water for 24 hours prior to adding it to the tank. My
> question is does anyone know of a computer program that I can use to make
> calculations of how much of each to add? I can do it manually, adding a
> little at a time, but it would be nice to be able to calculate it in
> advance in order to approximate what is needed so that it doesn't take so
> long to do or use up the expensive test kits. Another question. Since I
> am going to add calcium chloride (turbo-calcium) and sodium bicarbonate,
> should I also be worried about adding magnesium to the make up water?
>
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>I've been reading up on RO this evening and found several references that
>say that RO water can be more acidic than tap water (lower pH) because RO
>membranes do not reject CO2. This concerned me since I've been having
>water quality problems for some time and thought that it might be a problem
>with my sea water not having enough calcium. I bought a Nutrafin pH test
>kit and a Nutrafin Calcium test kit. I got some interesting results. For
>the tap water, I got a pH of 7.5 with 60 mg/L of calcium. At present, the
>water in my marine tank has a pH of 7.5 (yes, I know it is too low) with
>calcium at 280 mg/L. The RO water has a pH of 5.0! Calcium was
>essentially 0. I don't know if it is normal for the pH to be so low in RO
>water, but I suspect that adding this water unbuffered to my aquarium is
>the root cause of my problems (thankfully, I have quite a lot of sea sand
>in the tank, so it does prevent a pH crash below 7.5.). I understand that
>RO units do not always result in a substantial drop in pH since it depends
>on the amount of dissolved CO2 gas that is present in the feed water.
>Apparently, my tap water has a high CO2 content.
>
> This is a good argument for strict testing of make up water, especially
> since, in my case, I never tested the pH of the RO water, assuming that it
> was neutral (which it is obviously not). I plan to start adding sodium
> bicarbonate and calcium chloride to the RO make up water in the future,
> and aerating the water for 24 hours prior to adding it to the tank. My
> question is does anyone know of a computer program that I can use to make
> calculations of how much of each to add? I can do it manually, adding a
> little at a time, but it would be nice to be able to calculate it in
> advance in order to approximate what is needed so that it doesn't take so
> long to do or use up the expensive test kits. Another question. Since I
> am going to add calcium chloride (turbo-calcium) and sodium bicarbonate,
> should I also be worried about adding magnesium to the make up water?
>