Sand

[leehardy9]

hi all ive had my tank set up now for 4 weeks got play sand in washed very well and it was clean for 3 weeks now i see the sand going a greeny colour. how can i clean it

 

[fluttermoth]

It's probably algae growing on the top layer. Give the sand a good stir every time you do a water change and it shouldn't be an issue.