Cloudy tank before lights?

[LxHowler]

Hello, so I am not really new to saltwater and have delt with cloudy tanks before but this one had me a little bit baffled.
So when I get up in the morning my tank appears clean, I know that having no light on will make it look cleaner, when the light comes on the tank clouds slightly. It looks like something is floating around in the water, I thought this could be percipient but after testing the water all of the perameters are normal and no noticeable swings. After the lights have been on for a few hours the tank clears and appears to be crystal clear again.
I have been running carbon on it and that appears to make no difference.
Does this sound like a bacterial bloom as the tank is only a few months old?
Tank is a fluvial Evo that I got for free from a friend. Perameters are
Ammonia: 0
Nitrite: 0
Nitrate: 10
Phosphate 0.06 (slightly higher than normal)
Dkh: 8
Magnesium: 1300
Calcium: 420
Any advice would be welcomed. Everything is the tank is still looking healthy and showing no signs of stress. The tank is still fish only at the minute

 

[Doctorgori]

sand? or bb?

 

[LxHowler]

sand? or bb?

Sand bottom about 1 inch deep but it is quite coarse sand and doesn't look like it is blowing about in the flow.

 

[Doctorgori]

long shot/low probability but you said floating, can you cut the flow leave one end lit and make sure the cloud is not swimming? I mean occasionally that happens..but I’d bet on bacterial.

 

[LxHowler]

long shot/low probability but you said floating, can you cut the flow leave one end lit and make sure the cloud is not swimming? I mean occasionally that happens.

Yeah I can do that I will try tomorrow when my lights come back on. I just found it odd how it disappears after a few hours.