another boring pH question.....but i dont have a clue

[millym]

hi
checked tank levels this morning. ammonia 0,nitrite0,nitrate 10 BUT the pH which has always read 8 is now 7.8. is this a problem???? we have put medication in the tank for velvet/slime disease(about a week ago) but nothing else new. we've had the tank going for about 4 months & we cycled it properly etc. none of the fish seem to be acting weird all seem to be quite happy.but we did lose a danio this morning(ive put a post about it in 'unhealthy fish forum', he had fungus on his tail though)

what can cause the pH to change??? or is it the water supply???
any clues most helpful
thanks

 

[Terry]

The ph change that has happened in your tank is not a problem, if the change has happened slowly in your tank then the fish would have adapted to it as it was happening.
Have you put anything in your tank that is new,( i don't mean fish ). This can sometimes make a change to your ph level, The ph reading you have now is ok for the fish that you are keeping. What are your kh and gh readings this can sometimes change your ph.

 

[loganj]

How often are you doing water changes? The biological activity in the tank produces acids that will eventually overcome the buffering capacity of the water which will result in a drop in pH.

 

[millym]

thanks!
we do a 25% ish water change every week. havent got tests for water hardness but i know london water is v hard(apparently), we'll get some.
fish seem fine. we did put velvet/slime med in but im sure it says it doesnt affect any water parameters.