What is your phosphate management routine?

[Myka]

The "I have never had a PO4 reading" option is quite irrelevant because I doubt anyone who voted for that option used a D-D Merc kit or another high sensitivity kit. A "zero" on a Salifert or Elos kit is not actually zero, it is simply "undetectable" with those low sensitivity kits. Even if you got a "zero" on a D-D kit, it is highly unlikely that it really is zero, it is also "undetectable" with the D-D kit. PO4 can also be taken up by algae in such amounts that there is little left in the water column to test at any given time.

Originally Posted by marie

The more animals and plants you have living and growing in your system, the more phosphates get taken out of the water column.

Precisely. If there is more phosphate in the water column than the plants (both "good" and "bad") and animals can take up then it becomes a poison of sorts. We don't like nuisance algae and cyanobacteria so we try to lower phosphate to the level that our plants and animals can handle. We have many methods of lowering phosphate; GFO, carbon sourcing (VSV, Fauna Marin, Zeo, etc), and competitive elimination (chaeto).

Your test kit (any kit) will only read the amount of phosphate in the water column that exceeds the demands of all the organisms in the tank. If you have nuisance algae, cyanobacteria, and/or chaeto growing in your system this expresses the PO4 difference between the kit's reading and the demands of the "good" organisms in the system. If your test kit is "not detecting" phosphate, and you have nuisance algae you do have an excess of phosphate.

Nitrate also plays a role, but we are discussing phosphate here. The two are usually quite intertwined, and in most discussions aren't of significance to differentiate.

Personally, I gave up my GFO. GFO has never been in my new tank. So I voted:
"I run a ULNS" [Zeovit, just starting the nutrient lowering full system]
"I test PO4 frequently" [with Salifert it is "undetectable", and has been so since shortly after the tank finished cycling]