Tan,

Strange that you don't get carpet algae growing by now. Is the place enough of sunlight?

I'm using a plastic tub at the moment and normally I use a 3M hard sponge (Green) to rub the surface to score it a bit for better surface finishing to ease the algae growth.

I only have morning sunlight till 11am.

Cheers.

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Japanese Ranchu is another ball game