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[APD] Substrate, PO4 and algae

Hello folks!

Back in the days I didn't know of the estimative index I
sometimes used the equivalent of Jobe-sticks (Pokon-sticks)
with NPK. I also have very small amount of peat and
clay under the substrate (ordinary plain gravel).

Most of the sticks, peat and clay have been vacumed
but some probably still is left down there.

History: A half year ago I got a decent JBL PO4-test
kit and noticed how the PO4-level raised to 1-2 ppm
a couple of days after each 50% wc. With extreme
vacuming I managed to remove this problem. 

Nowadays my PO4-levels is not measurable
with my test-kit. It grows very well though.

But as a true fanatic I always need faster growth,
so I sometimes try to dose KH2PO4.

310 litres, 0.7 watts/litre, pH 6.0-6.5, alkalinity 2-4, total
hardness 6-8.
KNO3, K2SO4, MgSO4, Micros as recommended.
The Fe fluctuates between 0.2 and 0.05 ppm between
each wc (I dose twice a week). The NO3 fluctuates
between 5 and 15 ppm and I have a hard time
finding the right KNO3-dosage. My fish seems to
provide a whole lot of N (50 Rasbora espei, 
7 Chocolate gouramis, 2 SAE:s, 3 Ottos, 2 Rams).

The day after each KH2PO4-dose (0.5 ppm) my front
glass always have considerably more algae. When I had
Cyanobacteria they really boosted with each PO4-dose.
Especially if I forget to cover the aquarium at night as it 
otherwise gets direct and indirect sunlight in the mornings.

The plants didn't grow remarkably faster with each
PO4-dose. Perhaps somewhat more bud-development.

Question: Is it possible my plants get enough PO4 from
my polluted substrate and therefore not take any PO4 
from the water column?

// Daniel Larsson
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