pH swings w/ DIY CO2 and water changes

[fort384]

How big of an effect are pH swings going to have on my tank/inhabitants?

My tap water has a pH of around 7.8-8.0. My aquarium seems to test around 6.4-6.6 (higher in the morning/lower at night) now that I am using a DIY C02 system. So, when I perform water changes ~10%, I am adding high pH H2O to the tank which seems to have stabilized in the low 6 range for pH. Is this anything to be concerned about?

Also, my CO2 levels cause shifts throughout the day. When I calculate the CO2 ppm using KH and pH, the numbers vary wildly from around 100ppm CO2 in the morning, to around 15-20 ppm in the evening. The KH in my tank seems to hover around 7-8dKH, or 125-143 ppm. I have a drop counter that generally indicates high in the morning, and good most of the day after the lights come on, but I don't know how reliable it is because I am not using calibrated 4dKH solution in it yet (still need to make some...) My DIY system consists of 2 ~1L generators (yeast/sugar/baking soda) and a gas separator bottle. Should I be disconnecting one or both of the bottles at night to prevent the drastic pH shift that occurs from the CO2 saturation, or is this something to even worry about? Any advice would be great.

Here is a link to my Aquarium Log that shows the results of recent water chem tests.
http://www.geocities.com/pricex2000/masterAQ.xls

 

[Purrbox]

It's generally agreed that shifts in pH due to CO2 levels will not harm the inhabitants of your aquarium. However if the CO2 levels get overly high they can cause problems with O2 absorbtion. If your CO2 levels are getting upto 100ppm then that could be a cause for concern. Watch your fish closely in the mornings for signs of stress. If you see them at the top of the aquarium gasping for air, then you'll probably want to add an airstone and set it on a timer to run at night to gas off the extra CO2. It's also possible that you could be having problems with BBA soon as your CO2 levels are dipping below 30ppm. Depending on the size of your aquarium you may want to add an additional CO2 generator to help stabilize CO2 levels.

 

[fort384]

I added a 7" bubble wand that will kick-on after the lights go out. Hopefully that will stabilize the CO2 some. This hobby is getting expensive.

 

[fort384]

Well that worked about as good as it could. With the bubble wand running while the lights were off, I tested the CO2 (via KH and pH) this morning: came out to about 30 ppm. I tested it again when I got home from work, about 8 hrs into the light cycle, and it came out to 45 ppm. If it stays in this range with this new setup, I will be a happy camper. Much better than the 100+ CO2 readings I was getting with no aeration at night. pH is now holding stable at around 6.6, both day and night. Thanks for the great advice!

Even got some pearling today on my Java Ferns! Now if I can just get my riccia to pearl - looked amazing when I bought it at my LFS, bubbles all over it. It is growing like crazy, but not pearling...