If you think you.ve seen bad BGA, take a look at this; http://gizmodo.com/get-lost-in-the-swirling-green-seas-of-a-massive-algae-1728939083
The narrow, crinkly leaves look more like A. longiplumulosus than A. ulvaceous, and the flower colour matches, but both of those species normally...
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Only if the heated water can flow along to the thermostat end of the heaterstat.
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