I think you may want to see what is in the tap water you muse first.
Many folks there have higher PO4 and NO3 in the tap water.

So you may want to account for that.
Generally, algae is due to poor dosing and mostly CO2 issues.

I'd not worry about the PO4 going too high, I honestly do not know what too high might be. It's not toxic to fish and does not induce algae.

However, when you do water changes, this will lower the PO4 down.
So will active strong plant growth.

EI is a starting point for non limiting dosing of nutrients.
It does not imply the CO2 is a factor, so that must be non limiting for the light intensity.

You can reduce or remove KH2PO4 dosing to reduce the PO4 level if you wish.
Or you might reduce the KNO3 dosing to reduce the NO3.
Really up to you, it's a choice based on your own needs and tank.

If you dose 6ppm per week of PO4, the maximum possible build up will be 12ppm if no PO4 is used and you do 50% weekly water changes with tap that has 0.00ppm of PO4.

mg/L = ppm.

A 1/16 teaspoon only weighs .3 grams ,so 3x a week would = .9 grams.
1 teaspoon weights about 4.8 grams for KH2PO4, not 6.
At least the KH2PO4 I use.

Chuck's cal also states the weight at 4.8 grams per teaspoon for KH2PO4.
This means about 7.5 ppm per week of PO4. This assumes no uptake etc and no precipitation.

Differentiating smaller amount of KH2PO4, 0.3 grams is not much or 1/16th of a teaspoon, you have a lot of user error.

If you want more accuracy, you can make a dosing solution and dose that way, however, this method works fine using dry dosing as well.

Even if you have a bit rich PO4, the KNO3 dosing is generally what most focus on modifying.

Regards,
Tom Barr