Brown Dirt .... Help

[alljass]

Hi all,
I need your help in the following; I have set up my marine tank one year ago I introduced some fishes last year before the cycle, as the pet shop guy told me ( yes I learnt it the hard way , waste of money and some poor fishes had to suffer) . After suffering all that I stopped introducing any fishes in my tank and left it for almost a year as I had to travel. Two months ago I introduced new fishes to the tank everything went great; fishes are alive and moving normally. Yet, am suffering from one thing, the brown dirt. This brown dirt shows on the glass of my tank and the sand every few days. Every time I clean the glass by whipping it with a sponge it shows again after 2 - 3 days. It’s annoying I can’t get rid of it especially when it is all over the sand. I t can also be removed by whipping it with my finger.
The lighting in my tanks works for approximatly 8 hours
Could someone please help me with that? What is this and how can i get rid of it? Cleaning it won’t work as it re appears every few days. I tried changing 20% of the water, yet the same.
Please help me with that anyone
I have uploaded few pictures that might help

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[Grizz]

Diatoms cut back on feedings up your PWC's it will pass dont worry it happens to nearly every one

 

[alljass]

Thanks alot, this is great news

will watch the feeding .

do you know how long it usually takes ? and how often I should do PWC's?

 

[Grizz]

last one i had cleared up in 2 weeks PWC's should be based on the water parameters I did 10-15% 2x a week untill i got every thing under control now i do a 10g pwc weekly(90g)and have no problems. It's all about the water