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PO4 and red algae
Since it was I who started this latest PO4 thing (again) - I want to make a
few things clear:
I don't believe the PO4 "killed" the algae in my tank per sea.
This tank I spoke of with the particularly bad red/staghorn (as well as
various other algae) was a high light (220W PC at 5500K), pressurized gas CO2
injected 75 gal. tank with a pretty fair amount of N present at all times
Looking back now, I realize that the reason N was present "at all times" was
that it wasn't being used. Having read and believed the prevailing theme of P
encouraging algae that was so prevalent in the literature - I, like many
others, had chosen P as the limiting factor in this tank.
However, I went a bit overboard.
I figured if limiting P was a good thing, then eliminating it entirely would
be even better. I even went so far as to install phosphate sponges, and
having also purchased the rather $$ LaMotte low range phosphate test kit, I
took great pleasure in un-measurable levels of P.
Unfortunately, this supposedly limiting condition was lost entirely on the
algae for it continued to thrive.
I also tested for NO3, finding it odd that the level barely fluctuated
between water changes. That right there should have told me something - N was
not being consumed and with all that light, plants and CO2 - it certainly
should have been.
When I finally added the P (as KH2PO4) - bringing the levels first to about
.3ppm, the tank started sucking down N like a sponge. The red algae
disappeared almost overnight and within a month it was hard to find algae of
any sort present.
Were the plants now able to "out compete" the algae for available nutrients?
The plants did begin to grow at an incredible rate but I tend to doubt this
nutrient competition thing. This has been said and done before by many others
but I'm currently maintaining levels of all nutrients and traces in excess
(measurable amounts) within the water column so it's available to all.
N at 5-10ppm, PO4 at .5 - .7ppm and both are being consumed at 1/2 tsp and
1/8th tsp a week respectively. "K " I add freely along with plentiful
iron/traces neither of which I test for. Since plants are growing and algae
is not -- what's up?
Interestingly, I know there's still algae present in this tank -- a puff ball
of silver gray way back on the underwater spray bar, a touch of green hair
here and there on the driftwood, a spot of green dot on the sides near the
bottom where its hard to reach with my scrapper. They're all present and
available to multiply and spread -- but they don't anymore.
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