Lisa- here is an interesting bit that may shed some light on your hair algae with zero phosphate readings:
As long as the speed of phosphate removal is greater than the speed of production, all nuisance algae will eventually have to die off, as the phosphates are removed from the sytem.
The two main things that seem to confuse aquarists, are that:
The resulting die-off of algae takes time
Zero test levels from the water column is not the same as zero production, or uptake, of PO4
The aquarist needs to enable the system to dump phosphates BEFORE they can get used by algae; if 5ppm of PO4 is produced, and 5ppm uptaken by algae, one will still test a level of zero, as this only measures 'excess' that builds up in the water column.
The first, easiest way, to eliminate one major source, is via an RODI unit for water processing.
The second, is to use a phosphate sponge, like phosguard, or rowaphos.
It usually takes a combination of both, to achieve a 'quicker' result, though water changes,good skimming, etc., can achieve the same end,over a longer period of time.
The hobbyists also needs to understand that in addition to the daily production of PO4 by the life in the system, the phosphates introduced either via the source water, or livestock 'surges' (like when placing an amount of live rock , and it's subsequent 'die-off' occurs in a system) need to also be removed.
Since algae require phosphates to grow and thrive, PO4 removal is not only the true root 'cure', it's also the least complicated 'treatment' around, for dealing with nuisance algae.
Algicides just recycle the PO4 back into the system, to feed more algae.
'Clean up crews' (especially snails) merely recycle the algae, releasing the PO4 in their poop, to begin the process anew.
vitz
