low pH with good alk and cal. readings

[rayjay]

I think I'm missing something in the alk-pH relationship just when I thought I'd had it somewhat understandable.
With the problems I had with the pH in the home made salt mix, I decided to get new pH standards because mine were old, and all my tanks pH and new I.O. mix aged for 1 day, measure in the 7.7 to 7.8 range when calibrated with the old standard solutions. I hadn't worried about it on the asumption the standards were out of range.
The bad part is that now, with new chemicals from Ricca, I still get the same pH readings on everything, and the new standards agree with the old ones.
Now, what I don't understand is, my I.O. is just over 24 hours old, the calcium level 355 and the dKH is 11, how come the pH is reading 7.7?
I tried adding small amounts of the baked baking soda solution to bring the reading up to dKH of 13, but the pH is only at 7.73 after that.
I have been experimenting before this batch with aeration and with aeration using air from the indoor exit tube of my HRV which brings about 93 litres/sec into my basement where all my systems are set up.
The variations never were more than about .1 or .2 with indoor aeration over non aerated, and .3 max between indoor air and that incoming outdoor air on aerating the previous batch of I.O..
I tried pushing the dKh higher to 15 but all that did was precipitate calcium, and didn't really make a noticeable difference in the pH reading.

 

[Randy Holmes-Farley]

It is not unusual for new salt water to have a low pH, and the reason is excess CO2 in your home air. Any "correction" that you make will only be temporary unelss you add something continually (like limewater), or reduce the amount of CO2 in the air.

Personally, I don't bother to measure or adjust the pH of water change water. It is not something that needs to be matched, IMO.

 

[rayjay]

Thanks for replying.
It's not just my new salt water, but all my tanks as well that have this low pH.
I shouldn't have a problem with excess CO2 in there with outside air being pumped in at 93 litres/second should I? That's a lot of air.
My tanks get approx. 22 litres of full strength limewater nightly.
Aeration with an air pump sitting directly in the flow of the incoming outdoor air, does not appreciably change the pH. If there was excessive CO2 in the indoor air I would expect this aeration with outdoor air to bring the pH back in line both with new salt water and existing tank water. This has been repeated many times with new and with tank water from my various tank systems.

 

[Randy Holmes-Farley]

I shouldn't have a problem with excess CO2 in there with outside air being pumped in at 93 litres/second should I? That's a lot of air.

93 liters per second? Yes, that is a lot of air. Are you sure that is correct? That is like opening a high pressure cylinder.

 

[rayjay]

Yes, I have a lifebreath, 300DCS double cored HRV which is on maximum output of 93 litres/sec. as measured with contractor test equipment.
I had to purchase this because of the approximate 1000g of open water in my basement with all the tanks, my brine shrimp operation and the mysid operation, not to mention containers with new salt water and containers of aging tap water.
It is a double core unit, the largest available for home use without buying a commercial unit.
This is the specs on it. PDF scroll to page 10 model 300DCS.

HRV MODEL 300DCS SPECIFICATIONS

 

[Randy Holmes-Farley]

If that 93 L/second was coming from outside, then it seems unlikely that the indoor Co2 is especially elevated, but that can be checked with the aeration experiments that I describe here:

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

Most likely, the water itself is just not being adequately purged of the excess CO2 in it, and more aeration may help. Again, the aeration test will show that to be true (or not).

 

[rayjay]

I've been doing the aeration tests now for quite some time and have not had any significant change in pH either from aerating with room air or with air from the outdoors. All systems water tests similar each time.
Most of my systems have a large countercurrent protein skimmer on them, where the air stone is 2"X2"x7" and has a bore of 7/8". They are all driven by 2 Thomas linear pumps and each skimmer uses approx. 1 CFM of air. (some variation with each airstone)
The one in the picture is just turned up a little too much, but you can get an idea of the air volume these skimmers use.
Problem is, the couple of tanks without skimmers have the same test readings as the ones with these skimmers.

 

[Randy Holmes-Farley]

I've been doing the aeration tests now for quite some time and have not had any significant change in pH either from aerating with room air or with air from the outdoors. All systems water tests similar each time.

If the pH is in the 7's and the alkalinity is 2.5 meq/L (7 dKH) or higher, then aeration with outside air should raise it. If it does not, then either the aeration test was inadequate, or the pH measurement is off.