water quality

Question
Hello - i have had my tank for about 3 months now and currently i have 8 glowlights, 6 neon tetra'a, Bulldog plecy and 2 Khuli loaches. I check the water regulary and it was always around the upper end of the ph scale but just recently when i checked it again it was right down the bottom (acid) end of the ph scale.
i was just wondering why it might have changed so rapidly.
i have done a few little water changes hoping the ph goes back to normal soon.
i was wondering how to keep a balanced ph in my tank. and aslo i dont have any ;ive plants in my tanks just plastic ones. would a live plant help the ph.
also when the ph was low the water was cloudy..
any suggestions of how to keep the ph balanced. and what effects the ph?

thankyou Hannah

Answer
Hi Hannah
What size tank is it?
How often are you changing the water?
When you do change the water, are you using a gravel vacuum/syphon?
Do you know what the ammonia, nitrites, and nitrates are reading?
And, do you by chance have an undergravel filter running?

Christy