I guess I should ask; what are common phosphate numbers to see? What is a reasonable number. I have the Hanna low phosphate tester, just tested the water that my Pukani is curing in, and it read 0.04.
Most people aim for 0.01 to 0.03 ppm phosphate. Levels above that risk algae problems and may slow some hard coral growth,a nd levels below that can begin to starve corals if low enough.
Here's one article where I discuss it:
https://www.reef2reef.com/threads/o...-reef-aquarium-by-randy-holmes-farley.173563/
from it:
Phosphate
The "simplest" form of phosphorus in reef aquaria and in natural seawater is inorganic orthophosphate (H3PO4, H2PO4-, HPO4--, and PO4--- are all forms of orthophosphate). Inorganic orthophosphate is the only form of phosphorus that most test kits measure, including the misnamed Hanna "phosphorus" checker. Almost none of these kits measure organic phosphate, as is present in proteins, DNA, and phospholipids.
The inorganic phosphate concentration in seawater varies greatly from place to place, and also with depth and with the time of day. Surface waters are greatly depleted in phosphate relative to deeper waters, due to biological activities in the surface waters that sequester phosphate in organisms. Typical ocean surface phosphate concentrations are very low by typical reef keeping standards, sometimes as low as 0.005 ppm.
Absent of specific efforts to minimize the phosphate level, it will typically accumulate and rise in reef aquaria. It is introduced mostly with foods, but can also enter with top-off water and in some methods of calcium and alkalinity supplementation. Rarely does one need to look beyond foods as the primary source, however.
If allowed to rise above natural levels, phosphate can cause two undesirable results. One is inhibition of calcification. That is, it can reduce the rate at which corals and coralline algae can build calcium carbonate skeletons, potentially stunting their growth.
Phosphate can also be a limiting nutrient for algae growth. If phosphate is allowed to accumulate, algae growth may become problematic. At concentrations below about 0.03 ppm, the growth rate of many species of phytoplankton, for example, depends on the phosphate concentration (assuming that something else is not limiting growth, such as nitrogen or iron). Above this level, the growth rate of many of the ocean's organisms is independent of phosphate concentration (although this relationship is more complicated in a reef aquarium containing iron and/or nitrogen sources such as nitrate above natural levels). So deterring algae growth by controlling phosphate requires keeping phosphate levels quite low.
For these reasons, I recommend that phosphate should be kept at 0.03 ppm or lower. Whether keeping it below 0.01 ppm will yield substantial additional benefits may depend on the specific aquarium, but that is a goal that some aquarists are pursuing with various ways of exporting phosphate. It is also possible to drive phosphate too low, which can result in pale corals. In such a case, allowing phosphate to rise a bit, or providing the corals other foods, may be very useful. On the other hand, while they are few and far between, there are a small number of very nice aquaria with VERY high phosphate levels (above 1.0 ppm). Exactly how these aquaria avoid the problems that other aquaria suffer at high phosphate is unknown.
The best ways to maintain low levels of phosphate in normal aquaria are to incorporate some combination of phosphate export mechanisms, such as growing and harvesting turf algae, macroalgae or other rapidly growing organisms, using foods without excessive phosphate, skimming, using limewater, using phosphate binding media such as GFO (granular ferric oxide; always brown or black) and using organic carbon dosing (e.g., vodka, vinegar, biopellets, etc.) to drive bacterial growth
