Low pH?

[Cearbhaill]

Is it normal for RO/DI water mixed with Instant Ocean salt to result in a pH in the 7.8 range?
Water has been mixed for days and is being circulated well.

This pH reading comes from both my newly set up tank as well as the water I am holding in reserve. New Salifert test. Lights are not on very much- ±4 hours a day. Room air is fresh.

The only alkalinity test I have is Red Sea (Salifert backordered) and it reads "normal to high".

My TBS live rock was put in Wednesday evening- as of yet no ammonia or nitrite readings.
How much should I worry?
Should I adjust the tank water pH?
Should I adjust the pH in the reserve water before I do a water change?
If so- what is recommended to use?

[OrionGirl]

I think you will want to bring the pH up a bit. I probably wouldn't worry much until the tank has cycled, since tht process will have some affect on it, and the slightly lower pH means you'll have less toxic ammonia (though not by much!). Then, you may want to look into increasing the buffer. A baggie of crushed coral may help--but test your alkalinity as well.

[mogurnda]

A few ideas, none particularly satisfying:
-Too much CO2 from all the live stuff on the rock. You can test this by putting some of the water in a container and aerating vigorously. The pH in the container will increase if there is excess CO2. This can be solved with more circulation.
-Organic acids from decomposition. Doesn't seem likely since you aren't seeing much ammonia or nitrite.
-You can try increasing your alkalinity/pH by adding some baking soda, but be somewhat careful. Since you don't know your alkalinity precisely, you could go too far.

In the short term, I don't think that pH is a huge problem. It does indicate that something is not quite right, though. IO has always given me a pH around 8.2 with RO water.

[Cearbhaill]

Seems I might not have a problem.
Habib from Salifert saw my post, verified that my test kit was one of a "bad batch" and is sending me a new kit.
I can't say enough about a company that goes to such lengths to see that their customers have good product to work with. I didn't even post in a Salifert forum- he just happened upon my question and came forward. I am so impressed!

At any rate I still have no ammonia or nitrite, everything looks good, so I am trusting that RO/DI+IO= OK.
I am not one to add anything to an aquarium unless I see a clear need, and I'm certainly not there yet.
Let the cycle continue.