Ph Issues Again

[GouramiFanatic]

I tested my Ph level again late yesterday and it came back as a very yellow looking green that didn't match either 6.0 or 6.4. Unfortunately, it was to late to do anything so I did a water change first thing this morning. None of the fish died overnight and as a matter of fact, they all look really good.
I've been planning for a while now to add a small school of YoYo Loaches, but I don't want to add them until I know it's safe to. I can't figure out why my Ph keeps dropping. It used to test at a consistant 7.0, but then one week it dropped to 6.4. I did a water change a week or so ago and it tested at 6.8. Now it's back down once again.
The tap water tested at 6.8 right away and again at 6.8 when I left a sample sitting overnight. I haven't added any new fish or decorations to the tank other than an air stone which was added after the first Ph drop. I've cut down on the amount of food that I've been feeding. Also, when I did the water change this morning there was very little debris sucked up from the python. The very first water change since I noticed the Ph drop sucked up a LOT of debris. Now my questions...
Why does my aquarium's Ph keep dropping?
What should I do to fix it or does it even need to be fixed?
Is it safe to add the YoYo Loaches?
Thanks,
- Mandy

[malkore]

Mandy,

what is your tap water pH, both freshly taken, and rested overnight?

With changing seasons, water companies will add things to the water to make it more 'suitable' to the climate.
Biggest thing people notice is a slightly lower tap pH in the cold months, because cold water can hold CO2 more readily, and CO2 creates carbonic acid which lowers pH (and that's the main reason you let water rest before testing, so CO2 can outgas and pH can be read accurately)

[Johnmc]

Mandy,

I have had almost the exact same issue- 46G tank, Ph is 6.9 from of the tap, PH dropping to 6.3. What has worked for me is adding a cup of crushed coral to the filter. It has stabilized my PH at 7.2. Be careful when adding crushed coral though. A little bit will go a long way.

Cheers, John