Thanks for your reply ...

Tanks have been there for more than 6 months now with same water and substrate and the issue has started from 2 months back, if I donot run my filters and water is somewhat still with the aeration running then the wtare slowly clears out in a day or two, however you can see the same dirt collecting amongst the milfoil and also you can see a layer of dirt on the substrate.

Fishes are doing fine ...

Regards