Not in marine plants really, Ca/Mg and KH are nutrients, the CO3/Ca/Mg are all needed, especially Ca and CO3.

Many macro's are mainly CaCO3 ......just like coral skeletons.......except macros assimilate and grow at least an order of magnitude faster than hard corals.

So they can pull a lot out of the water column.

Generally: Ca, CO3/KH, and NO3 and traces are the main players.

While some and myself included have added PO4, I think the systems can do quite well without dosing it as most systems are well adapted to P limitation.

Even here, I think adding say 0.1ppm PO4 from a KH2PO4 stock solution, or even 0.05ppm, 2x a week is ample along with feeding for most any tank.

IME, adding .4-.5ppm of PO4 causes some diatom blooms, but.......that was just 2 tanks, hardly a consensus and I just have not done enough dosing and measurements yet on marine macro tanks to say much.

But.........I would stick conservative abd slowly work your way up, but rather than focus on how much/diatoms etc, focus on the health of the plants.

That is the important thing/observation.

Regards,
Tom Barr