KittyKat
Aquarium Advice Activist
The average, well looked after, tropical community fish can go without food for two weeks without problems. Some mouth brooders will even go up to 4 weeks without food while holding young 
The pH dropped probably because your KH is low, which means that your water isn't that buffered. The reason it crashed is probably directly related to your filter cycling, the process created H+ (acid) ions, see Nitrification - Wikipedia, the free encyclopedia for more details.
Be careful: pH of 6.2 is approximately 6.5 times lower than 7.0 because it's on a logarithmic scale. My immediate advice is to measure your pH after the new (tap?) water has sat in a clean and rinsed glass for 24 hours and to do a few water changes today and tomorrow until the pH is back at 7.0. For example, something like this should be relatively safe:
* now: 10% water change
* hour 1: 15% water change
* hour 2: 15% water change
* hour 3: 25% water change
* hour 4: 25% water change
* hour 5: 35% water change
…etc, until you get up to 95% water change. This should slowly return your pH to a safer and more effective 7.0. Apart from the fact that pH crashes are very harmful to (and can kill) fish and crustaceans, filter bacteria also don't work very well at low pHs.
My slightly longer term recommendations are to do larger daily water changes for the duration of the cycle, get a KH and GH test kits (if someone's KH is low enough for pH crashes, then I think they should test it every 1-2 weeks in the long term anyway) and add a coupld of crushed mussel shells to the filter.
Once the filter is cycled, the pH should remain relatively stable, especially in a planted tank.
The pH dropped probably because your KH is low, which means that your water isn't that buffered. The reason it crashed is probably directly related to your filter cycling, the process created H+ (acid) ions, see Nitrification - Wikipedia, the free encyclopedia for more details.
Be careful: pH of 6.2 is approximately 6.5 times lower than 7.0 because it's on a logarithmic scale. My immediate advice is to measure your pH after the new (tap?) water has sat in a clean and rinsed glass for 24 hours and to do a few water changes today and tomorrow until the pH is back at 7.0. For example, something like this should be relatively safe:
* now: 10% water change
* hour 1: 15% water change
* hour 2: 15% water change
* hour 3: 25% water change
* hour 4: 25% water change
* hour 5: 35% water change
…etc, until you get up to 95% water change. This should slowly return your pH to a safer and more effective 7.0. Apart from the fact that pH crashes are very harmful to (and can kill) fish and crustaceans, filter bacteria also don't work very well at low pHs.
My slightly longer term recommendations are to do larger daily water changes for the duration of the cycle, get a KH and GH test kits (if someone's KH is low enough for pH crashes, then I think they should test it every 1-2 weeks in the long term anyway) and add a coupld of crushed mussel shells to the filter.
Once the filter is cycled, the pH should remain relatively stable, especially in a planted tank.
