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Re: Addition of K and reduction of NO3

I've just go through the process of reduction of NO3 by adding K2SO4 only.
My water supply in my house has high NO3 content more than 40mg/l measured
by the Sera Test Kit (probably due to the water tank in the roof top).

I once had a serious algae problem.  I starved the tank by adding nothing
and did not change water for a long time probably 2 months.  However, I
continue to supply adequate light, the NO3 level drops to zero.  Because the
plants and algae used up all the nutrient.

But most of the plant and algae die except some tough plant like Hygrophila
corymbosa, Rotala rotundifolia and  Limnophila sessiliflora.  I then started
to buy some fast growing plant again and rebuilt the tank.  Replaced about
1/3 of the tank with my tape water (high NO3 content).  The NO3 level
changed to 20mg/l< [NO3] <40mg/l (it is still too high).

This time I add no NO3 but I add MgSO4 and K2SO4 of  5cc and 10cc daily
respectively.  Then I measure the NO3 again after a week.  The NO3 drops to
5mg/l.  Then I change the tank water of 1/4.  The NO3 raise back to 10mg/l.
The NO3 then drops again to <5mg/l after few days.  I keep this cycle for
about 2 months.  According to my observations,  I know my plants did used up
most of the NO3 and I find no trace of ALGAE growth. [This is the greatest
achievement since it is the first time after I built the tank for 18

Today,  I add 5cc KNO3 and 10cc of K2SO4 to provide NO3 for my plants'
consumption.  But I will be very prudent of adding KNO3 as I don't want to
see the algae bloom again.  So close monitoring and the balance of nutrient
is very important!

My tank data - 120cm x 40cm x 55cm (240litre)
Lighting 150W HQI 2nos. (turn on 8 hours daily)
Few drops of JBL Ferropol daily to provide Fe.
CO2 supply with automatic pH control

However,  I have a question of how to adding Calcium as sometimes I see the
tips of growing point turn to brown.  I know the Calcium may be deficient.
I will put a tiny bit of CaSO4 (gypsum) in water or change some water, the
plant will grow some new tips.  But any better suggestion?


Matthew Chan