[karimwassef]

I think sand allows the accumulation of waste. Without sufficient motion or cleaning, this decay allows bacteria to take over. That's usually cyano. Algae has a hard time sticking to sand, so an unhealthy sandbed is like a buffet for dinos... They seem to coexist well with bacteria and this is an ideal zone. They consume the waste before it makes it up to the rocks and glass where algae can use it. Then, they slowly take over the other spaces... Consuming up as they go... Until they get to feast on any waste without leaving any space or waste for algae... Tank domination!!!

Just my theory... It works better with the war music in my head.

So... Either fix the sand or remove it.