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?


To give an answer to that we need to know a little bit mo carbonate
and permanent hardness of your tab water, its nitrate and phosphate
level (assuming that nitrite and ammonia are not present) and the
nitrate and phosphate level in your tank. It may also be useful to
measure the iron concentration, which is a marker for the supply of
trace metals required for plant health. A good trace element fertiliser
(without nitrate and phosphate) like Doc Kremsers (no affiliation) might
give your plants a head start over the algae. What is the stocking
level?

Fast growing plants like Cabomba or duck weed can lower nitrate
concentrations and thus fight algae. Note that high nitrate may well be
the cause of algae, in particular bga (something I have a running battle
with since my tab water is 40 mg/l nitrate due to agricultural
pollution). About 5-10 mg/ml is considered ideal for good plant growth
and algae reduction, phosphate should be below 0.5 mg/ml.

Moderate algae growth is not really a problem, after all we are running
an ecological system and not an operating theater. Excess algae are
unsightly, and in particular bga may produce poisons that harm your
fish. A good way to rid ones tank of bga is a dark periode of 1 week
(lights of and blanket over the tank). Plants and green algae will
survive, but bga is eliminated. You may also place a piece of net
curtain over the affected plants, bga are motile and will over a few
days move on top of the cloth for better light. They can then be removed
with the cloth. This is best done before the dark cure to reduce the
bio-load of decaying algae.

If your water is alkaline because of high hardness (the two usually run
together) you can either keep fishes that like such water, or you can
try to reduce hardness and pH. Mixing the tab water with demineralised
(usually by reversed osmosis) water is one option, filtering the water
over peat, the cones of _Alnus glutinosa_ (a tree found near river
benches) or oak leaves another. In either case be sure to reduce the pH
real SLOW, otherwise you may harm your fishes. Do not use chemicals to
lower pH, they often contain phosphoric acid which makes your algae
problem worse.

5 gal a week for a 90 gal tank is not enough water change, increase to
about 10-15 gal a week to ensure adequate water quality. I do 10% twice
a week, which seems to work nicely.