Of Algae and Diatom Filters, was orthophosphate

["Sharon Stewart" <sharon at stewartcentral_com>]

My diatom filter arrived. Yee ha! What a magnificent beast it is. I'm
glad I finally broke down and got it--sucked all the green water right
out of my tank. My 6-year-old said, "Mommy, what happened to all the
allergies?!" I bought the Vortex XL, and used the "pitcher method" of
charging the filter. It worked like a charm! Now, on to trying to keep
the green water at bay!

Thank you to Tom Barr, who was kind enough to answer my questions on the
orthophosphate that my water company adds to the water supply and
offered this advice for my algae problem:

"One of two things basically, either not enough plant growth(Not enough
CO2,
NO3 etc, or a spike, although a small one will do of NH4)
If you have a tank that produces say 1mg/l of NH4 a day and you never
measure any present due to ACTIVE HEALTHY plants, then there's no
problem,
but if the plants are limited, say by PO4, then the rate of uptake for
NH4,
NO3 etc declines.
GW is impossible to beat through nutrient limitation, you'll kill the
plants
first. GW need next to nothing to grow. I'm talking like less than
0.0003ppm
of PO4.......no one has a testing procedure or kits that is even close
nor
accurate enough to do this.

Once you kill/filter it, making sure there's enough NO3(Not NH4), K,
PO4,
Traces and most importantly CO2 will prevent any algae from coming back.
Anything that slows down N uptake is bad. Healthy plants are your best
defense against all algae. So grow the plants and cater to their needs."

I recently added C02 and started adding baking soda to up my KH--this
stopped my ph from swinging so wildly (once the ph swings were stopped,
my Bentos tetra came out of hiding. Poor guy retreated with the ph
swings).

Now for more questions: My NO3 was between 10 and 20ppm using the Red
Sea kit (I can't tell the pinks apart). Phosphate had measured 0, also
with a Red Sea kit. I'm not sure if that is correct or a problem with
the kit--with phosphate being added to the water supply, I would have
expected to measure something. I'm assuming I should start by adding
PO4--would the Fleet enema be a good enough source? How much should I
shoot for in a 38 gallon? (I happen to have sodium
tripolyphosphate--STPP--on hand. Am I correct in assuming that that is
not an appropriate phosphate source for a fish tank?) I also suspect a
potassium deficiency--I have potassium gluconate tablets for that.

Hopefully, now that the tank isn't filled with pea soup, the co2 will
have a chance to do its stuff. 

I appreciate the help!

Sharon S.