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[APD] woes with walsted type tank

Hopefully it is not inappropriate here, but rather than typing politics I
wanted to discuss something about aquatic plants...

I have several planted aquariums. One of them is a "natural aquarium" set
up following the principles outlined by Daina Walsted in her book "ecology
of the planted aquarium" This tank is a 20H mounted in a west facing window
where it received ~3h of sunshine / day this time of year suplemented by a
1x65w coalife PC which runs for 3 hours in the morning. the sunlight is
diffused and attenuated somewhat by 2 layer of bubble wrap which prevents
burning of plant leaves.

I was beginning to have problems with stunted plant growth and lots green
slime algae, so I tested the water and found 0 nitrates and lots of
phosphate. I started dosing 3ml excel /day + 5ml / day of the NP mix I use
in my CO2 injected tanks. this mix is 8tsp KNO3, 3tps KH2PO4, 16oz water.
Water here is extremely hard 9dKH, 20dGH, 77ppm Ca, 41ppm Mg. no recent
additions of fish or inverts to increase boiload, tank was healthy for
~1year before this. plants include hornwort, pond penny, crypt wentii,
amazon sword, corkscrew and contortion vals, a huge ludwigia growing
emersed out the back and across the window sill, and rotala indica. The
filter is a penguin mini which contains seachem purigen, a sponge on the
intake, and a biowheel.

when I started dosing, plant growth resumed, but  I started losing shrimp
and fish. After a month I am now down to 1 ghost shrimp and 2 fish in this
tank. I finally decided to do a more comprehensive water test and was
suprised to see measurable amounts of NH4 and nitrite.

 Walstad states in her book that adding nitrate to a 'natural' aquarium
would result in anerobic bacteria converting it back into nitrite and NH4.
Is this what is happening ?

if this is what is happening, why does this not happen in my co2 injected
high light cube with 6" of sand as substrate ? surely there are anoxic
zones in that substate if they exist in half that thickness of dirt and


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