Ph ??? IN SPS TANK

[Greg 45]

I have read to many articles on low ph . At this time my tank's low at night 7.9 , day time 8.1 . All articles say that this is ok. Everything in tank looks ok. Is there any reason to be concerned. There is a calcium reactor on system. The only thing is when mixing up new batches of water with ro/di water it only has a ph of 7.8. Is this the root of my problem . How can I raise up new batches of fresh water.

[JamesJR]

If you are concerned you might add a very small amount of baking soda to your RO/DI top off water to bring it's pH up to that of the tank but I wouldn't worry too much. Your tank sounds fine to me.

[PatrickJ]

I would raise it. Use Kalkwasser.

[Randy Holmes-Farley]

I would raise it, and recommend doing so if the pH is below 8, and if rapid calcification is a prime goal, to pH 8.2 or higher. That said, one can have a fine reef aquarium at pH 7.9, it is just more stressful to calcifying corals, especially if the alkalinity is also on the low end of normal. Limewater and more aeration with fresh air are the best ways to raise pH:

Low pH: Causes and Cures
http://reefkeeping.com/issues/2004-09/rhf/index.htm

The only thing is when mixing up new batches of water with ro/di water it only has a ph of 7.8. Is this the root of my problem .

No, that is not a contributor. from

Reverse Osmosis/Deionization Systems to Purify Tap Water for Reef Aquaria
http://reefkeeping.com/issues/2005-05/rhf/index.htm

here

http://www.reefkeeping.com/issues/2005-05/rhf/index.php#8

Final Effluent pH

Aside from the issues discussed above concerning the effluent’s pH when the DI resin becomes depleted, the final pH coming out of an RO/DI system should not significantly concern reef aquarists. Many aquarists with low pH problems have asked, for example, if their aquarium’s low pH may be caused by their replacing evaporated water with RO/DI water that they measure to have a pH below 7. In short, the answer is no, this is not a cause of low pH nor is it something to be generally concerned about, for the following reasons:

1. The pH of totally pure water is around 7 (with the exact value depending on temperature). As carbon dioxide from the atmosphere enters the water, the pH drops into the 6’s and even into the 5’s, depending on the amount of CO2. At saturation with the level of CO2 in normal (outside) air, the pH would be about 5.66. Indoor air often has even more CO2, and the pH can drop a bit lower, into the 5’s. Consequently, the pH of highly purified water coming from an RO/DI unit is expected to be in the pH 5-7 range.

2. The pH of highly purified water is not accurately measured by test kits, or by pH meters. There are several different reasons for this, including the fact that highly purified water has very little buffering capacity, so its pH is easily changed. Even the acidity or basicity of a pH test kit’s indicator dye is enough to alter pure water’s measured pH. As for pH meters, the probes themselves do not function well in the very low ionic strength of pure freshwater, and trace impurities on them can swing the pH around quite a bit.

3. The pH of the combination of two solutions does not necessarily reflect the average (not even a weighted average) of their two pH values. The final pH of a mixture may actually not even be between the pH’s of the two solutions when combined. Consequently, adding pH 7 pure water to pH 8.2 seawater may not even result in a pH below 8.2, but rather might be higher than 8.2 (for complex reasons relating to the acidity of bicarbonate in seawater vs. freshwater).