Phoslock is a modified clay product made from naturally occurring products lanthanum and bentonite. Lanthanum binds with phosphorus to produce lanthanum phosphate. Lanthanum phosphate is very insoluble and therefore once bound phosphorus remains locked up within the bentonite. Phoslock settles on the sediment and so long as there are active lanthanum sites it will continue to react with any phosphorus either released from the sediment or present in the water.
Phoslock is a focused solution – it directly reduces phosphorus levels but has no direct impact on nitrogen or chloride. By reducing algae levels it can have an indirect impact of the loss of dissolved oxygen attributed to decaying algae.
Phoslock is estimated to cost up to 50% more than traditional chemical applications such as aluminum compounds. The need for frequent periodic treatments means that the additional long term costs are significant. Do the benefits of Phoslock clearly justify the additional costs?
The manufacturer notes that Phoslock has been the subject of extensive ecotoxicity and other testing however some experts have expressed concern that there is not enough experience to be completely comfortable with the long term impact under continued use. Freshwater Research notes that it would be prudent to time the Phoslock treatment so as not to interfere with egg laying stages for amphibians and turtles, so there is some level of concern about possible environmental impact.
Therefore while Phoslock may provide an effective immediate solution for reducing phosphorus levels, more investigation should be undertaken to find complementary effective solutions that will minimize the future dependency on Phoslock for both financial and environmental reasons.