The problem with phosphate removal is that many sources can provide sufficient phosphates for algae; it takes very, very little to be enough. Managing phosphate levels is easiest on pools with DE or cartridge filters, low evaporation rates, and no leaks. The reason is that most utility water contains significant levels of phosphates. As a result phosphate remover must be added to the pool EVERY time you add fill water, unless you are filling from a well or other untreated water source.
There are two other problems.
1. The available tests are finicky and do not measure the levels of phosphates in incoming water, where PO4 > 1,000 ppb, well. It can be done, but requires PRECISE dilution with distilled water.
2. The phosphate removal products on the market are disappointing in quality. Only the Orenda PR-10000 product seems to offer a decent price/performance ratio.
That said, phosphate management seems to offer the ONLY relatively easy, side-effect free method of managing mustard algae in that fraction of pools that suffer recurring episodes.
=> Ammonia based products (Yellow Out, etc.) generate high levels of the VERY irritating monochloramine, and screw up chlorine management downstream of their use.
=> Bromide based products (Yellow Treat, etc.) are not especially effective against mustard algae, and make it impossible to stabilize the halogen (chlorine + bromine from converted bromide) residual, resulting in huge chlorine demand downstream.
=> Raising FC levels to 30 or 40% of the CYA level works, but not instantly, and can leave pools at levels that can bleach swimwear and some pool liners for days after treatment, depending on the initial CYA level
=> High levels of copper ARE effective, but they are ALSO effective at staining pools and turning hair green.
=> Borates help with other forms of algae, but apparently are only marginally effective with respect to mustard algae. However, other than cost, there is no downside to their use.
I just realized that I have been assuming people knew what I know, and have been failing to mention PHYSICAL BRUSHING OF THE POOL IS ESSENTIAL, regardless of which mode of chemical treatments for mustard algae you follow.
If you have mustard algae, you MUST brush!
