[cyfan964]

Do these need to be purchased? If I'm dosing a 10-gallon in small increments is it really necessary to test these?

 

[GTR]

There are several hobby kits on the market for PO4 but I never felt I could differentiate the color enough to feel I knew what the level was after I tested. I had a Hanna colorimeter for PO4 for a few years. It was accurate IMO but not necessary for FW so I sold it.
As for K I only know of two hobby test kits, I had one of them and even testing a known standard the color was way off based on what the manufacturer claimed it should be.

SteveU

 

[jmhart]

Neither is especially important to test for.

It's hard to get high K levels in a tank. PO4 too. The only real issue is if you have PO4 coming in with your tap water and you does heavy PO4 on top of that. Before buying a test kit you can just check your local water report for PO4.

 

[plantbrain]

Do these need to be purchased? If I'm dosing a 10-gallon in small increments is it really necessary to test these?

If you simply did a weekly water change and dosed, no testing would be required.

Water changes prevents anything from building up, dosing prevent it from running out. Simple concept, see EI dosing. For smaller tanks like a 10 Gal, might be easier to make a solution of ferts to dose easier instead of dry powders.

Regards,
Tom Barr