What is this and how can I stop it?

[Dan7575]

I have always from start had brown films on the sand but over the last 6 months it has started to develop into a thick layer of much that envelops the sand and every WC I have to siphon it off and end up losing loads of sand.

do you know what it is and how to stop it?

 

[eag]

Looks like at least two different things .. I think I see some red cyano on the sand in the last picture. I'm not sure about the first two pics .. but brown film makes me suspect something like dino

 

[Lavey29]

Full tank parameters please

 

[Dan7575]

Alk - 7.2
Cal - 430
Mag - 1350
No3 - 5ppm
Phos - 0.01

there is a little bit of cyano and in the middle of the tank what looks like diatoms which have never gone away, tank is 3.5 years old. The mucky stuff is more of a green colour and only forms in the spaces under the wavemakers where it seems are the dead spots where the detritus and bits of broken off coralline algae collects

 

[Remy123]

Most likely a cyano or slime algae. I would try increasing flow in those areas and see if it recedes

 

[RocketEngineer]

That looks like an area of low flow that needs a good siphoning. I would vacuum the sand in that spot with my next water change, being sure to either tumble it well or remove the sand entirely. Not the whole sand bed, just that small area. It’s likely low flow has allowed detritus to settle there and accumulate.