Hi Shane, Further to the No3Po4-X instructions we recommend reducing by 50% the dosage in the event of the Nitrate dropping below 1 ppm.
We first need to decide which route you are looking at, low nutrition or rapid growth ? either way stop using your gfo, however keep it ready for use again if needed, we sometimes see nutrient release from live rock so your Po4 may go up whilst establishing colonies of PHB's (Phosphate Harbouring Bactria) whilst we have zero Po4 it will be difficult to develope these bacteria as they need a food source of Po4 along with that within the No3Po4-X.
I'm going to suggest a very low dosage of No3Po4-X initaly of 0.25 ml per 25 gal/100 litre and also an increase in feeding, do not be scared to feed your fish No3Po4-X is very efficient and will quickly control the No3, Po4 does take longer as the PHB developement does take much longer.
It is important to set your skimmer to produce a wet skimate, this helps with the Po4 export, Po4 is consumed by the PHB's and when they die off laden with Po4 they are extracted by the skimmer.
You will see a change in skimate color from a dark green to a light golden tea color, this is normal so don't be alarmed.
Let us see your current Mg, Ca & Alk levels it is these that will set your No3 & Po4 levels.