[orcafood]

I'm excited to see the end result! I don't see a need to test n/p levels in a functioning reef tank. Calcium is linked to alkalinity thus I see measuring alkalinity as the optically testable parameter.

All reagents are dirt cheap if you know what your doing (why doesn't anyone sell there own testing kits). Any kit costs a few dollars to make tops.

I agree that colorimeters are the way to go. Titration would be necessary for any non-volatile molecule.