Lowering ph

Animal wrote:
I have a problem,(I guess if I didn't I wouldn't be asking a
question!),anyways,I have a 90 gall heavily planted freshwater community
tank that's been set up for 10 years.Because I've always had a mild amount
of algae,I was doing large (70 %)water changes weekly to try to eliminate
the algae, but in the last 6 months it's gotten worse.(I think it's
cyanobacteria)I don't think I over feed or the tanks over populated.
I started adding KNO3(potassium nitrate)to increase the nitrate and have
reduced the water change to 5 gallons a week and it seems to work but now
I've noticed the ph has risen to above 8!.The tap water is about 7+/- .To
confuse matters even more,I also have a well established 50 gall that I
haven't changed my normal routine(water change,feeding ,fishload,ect...all
the same as usual)and the ph in that tank is also over 8.


So my questions are would KNO3 raise the ph?
If it's not the KNO3 what could it be?
What is the best way to lower it and keep it down safely?




Try checking your pH in the morning, before the lights go on. If your
water is at all hard, the pH may rise during the day due to action of
the plants using carbon, thus reducing carbonic acid content of the
water. With KNO3 your plants will grow more and the effect may be more
pronounced. It's perfectly ok, although use of CO2 injection may
counteract the effect, I think.

I'd increase the water changes though. Tom Barr recommends big water
changes such as 50% weekly, and KNO3 addition etc. With your tiny water
changes the water may be becoming more hard due to evaporation...

Can't explain your 50 gal tank, though .

Finally, others have explained that you should let a glass of tapwater
stand for 24 hours before testing pH, because it may change due to
outgassing etc.