That pH drop is not unexpected.
The drop is pretty low, but it also may not be accurate.
Low pH is always caused by high CO2 in the water (if alk is normal) and usually that means high CO2 in teh home air (only other possibility is inadequate aeration).
If you want to use a two part instead of kalkwasser, you can get the same ph boost using a very high pH two part made from sodium hydroxide for the alk part.
This has more on CO2:
pH And The Reef Aquarium
http://www.reefedition.com/ph-and-the-reef-aquarium
from it:
The Aeration Test
Some of the possible causes of low pH listed above require an effort to diagnose. Problems 3 and 4 are quite common, and here is a way to distinguish them. Remove a cup of tank water and measure its pH. Then aerate it for an hour with an airstone using outside air. Its pH should rise if it is unusually low for the measured alkalinity (Figure 2). Then repeat the same experiment on a new cup of water using inside air. If its pH also rises, then the aquarium’s pH will rise simply with more aeration because it is only the aquarium that contains excess carbon dioxide. If the pH does not rise in the cup (or rises very little) when aerating with indoor air, then that air likely contains excess CO2, and more aeration with that same air will not solve the low pH problem (although aeration with fresher air should). Be careful implementing this test if the outside aeration test results in a large temperature change (more than 5°C or 10°F), because such changes alone impact pH measurements.
Process to test this theory --
1.) Recalibrated Apex pH probe, I believe its fairly accurate. Put it into pH of 7, it's 7. Put it in 10. It's 10. Calibrated using TC in Apex. I keep my tank at 77-78.
2.) Purchased a Milwaukee MW-101. Calibrated both probes in the same calibration solution. Put it 7, its 7, put it in 10, it's 10. Also used a lab grade mercury temp to set temperature correction at 25 degrees C.
3.) Place both probes into the same calibration fluid, they both agree on the same 7 and 10 pH ranges down to 0.01.
Where things start to diverge ---
4.) Do both probes agree in the tank water --
NO -- 7.84 pH (Apex) vs 7.94 pH (Milwaukee). I am not totally upset about a 0.1 difference but fine, as long as both instruments are repeatable? Right?! ---- Though I cannot understand why. Probe differences? Should I buy another APEX probe for the Milwaukee?
The Aeration Test -- "Rubber Meets the Road" ---
5.) Using the Milwaukee MW-101, performing the 1 hour long
outside aeration test moved the pH from 7.95 to 8.15. Performed at the hours of 10:30 PM to 11:30 PM. An increase.
6.) Performing the same test, but
inside near the tank results from the sample taken at 11:30 PM to 12:30 of a pH from 7.90 (new sample water taken from the tank) to 7.88. Picture of the apparatus attached.
7.) Moving the Milwaukee MW-101, back to the tank, the pH is time 12:36 to a pH of 7.86 to sit for 5 minutes for a stable reading. The Apex reads a pH of 7.76 units.
So what does this tell me?
With a stable tank alkalinity, indoor CO2 is affecting the pH of my tank. As seen from my outdoor aeration, the pH rises. Indoor test shows the pH stays almost the same. Though, my house is quite old (1968) with original awful windows, I have a skimmer pulling outdoor air, the CO2 is here. I could try a bigger skimmer to bring in more outdoor air. I can also use CaOH to raise my pH.
Will scrubbing CO2 fix my issues?
No. From my tests, I haven't seen a significant difference, with or without. Doesn't move the meter. Though I still need to try other brands of media that are reported to work better. I will try this again.
Also attached the pH of the tank water from the Apex - rapidly dropping as time goes along.
Any other observations? Suggestions?
