Oh My! Ph Crash!

[Man of fish]

A few days ago the water in my (10 gallon) fry tank started to go cloudy. Today is regular w/c day so I tested water as usual and the ph is at a 6.0!! From a 6.8 from last week. I'm in the process of a 90% change but what more can be done and is the cloudy water have anything to do with it?
All other stats are good
Ammonia 0
Nitrite 0
Nitrate 5-10

 

[Man of fish]

Did about an 85% water change 4 hours ago and now the ph is at 7.2.
Out of curiosity I tested my taps ph and it was > 7.6 so tested with high range and got 8.0. It always lowers within a day though so could this be bad?

 

[The Taffy Apple]

You may live in an area of soft water, therefore your water will have a low PH buffering capacity.
A KH/GH test kit will prove this..i got mine for about £4 off Ebay.

Terry.

 

[Man of fish]

I remember my results were 15 and 75 from about 2 months ago when used a test kit at a nice store. They used a liquid test.