Fishman holly crap. I was doing the same thing. Add me to the stupid club. I was cussing the cole parmer kit. I threw it away b/c the readings did not jive with my pH I was getting. Good news it motivated me to order a digitial titrator from Hach. It is way more accurate than anything out there. However it is not for the average pondowner with a (I think) $165 price tag. The reagents will not be much more than the cole parmer kit though.
Jake Bill has a good point. If not the low alkalinity then why can you not get a bloom. Make sure the ferilizer is water soulble. Fishman thanks for making me realize my stupidty
