The amount of dry Nitrogen from frozen foods varies considerably.

I've always been somewhat bemused that folks insist that the bioload or the food is some stable source they can measure(not you!, in general).

NH4 and total N are hard to measure what actually gets to the plant/macro or micro algae. It's hard for me to measure it.

Food can be measured for NH4, NO3 etc by dry weight. It's a bit involved, and the food itself varies batch to batch as well.

Most of the weight is water in frozen foods.
So it's not that suprising you still need more KNO3.

Regards,
Tom Barr