pH of emersed tank's water shifted!

I did a pH measurement of the main section of my emersed tank today and discovered that it has increased from 4.5 (measured 2 weeks ago) to 6.0! Reasons could be attibuted to the following:

1. lack of pH buffering substance in the water (I removed the bag of peat moss from the water about 1 month ago after confirming that the pH is low enough)
2. introduction of more fishes (added 01 betta, 02 croaking gouramis and 01 Aplocheilus panchax which I caught during my field trip) + increased feeding

I do not think I currently have cryptocorynes which require really low pH to survive (or do I???). I will have to closely monitor the entire situation before decided if further actions are required to be taken to lower the pH again. So pals, for those who wishes to have a low stable pH in your emersed cryptocoryne tank, think twice before adding fishes!