What causes sudden PH drop?

[imissmytruck]

I have been trying to figure out what caused my sudden PH drop. My mystery snail has developed a bad case of shell rot...the guys at my LFS says it's a lack of calcium in the tank due to a PH drop. The only thing I've done different was changed from Prime to Seachems Alpha from the AquaVitro line to control my Nitrate. (which were sorta high even for a REALLY planted tank.)

The Nitrate level dropped. Fast. I was very happy. But now I cant figure out why the PH dropped so drastically.

Any ideas?

and to answer the normal questions. All levels are fine BUT the PH. In a planted 55g. I change about 40 to 50% of the water weekly when I have the time to be on top of the game....never go more than 2 weeks. Now I actually have to wait for the next one to bring my nitrate level a little higher for my plants.

 

[aqua_chem]

Well, for starters, what is your pH? Do you have driftwood? What's your KH?

 

[imissmytruck]

The PH went down to 6.2 over night. About a week ago. The KH is 80 ppm. I had issues with high PH when I started so I did have several pieces of bog log, but have removed most of it.