water changes

[fish man]

How come after I do a water change 2 days later my sand and the sides of my tank have brown algae on them

 

[happyvac]

Because you don't use RO/DI?

 

[jakebtc]

probably, or maybe extended lighting period or phosphates or a combination

 

[beth]

Because your source water likely has silica/silicates and/or nitrates and/or phosphates. This would be food sources for diatom colonies. And the more they eat, the more they grow. This is one reason that we use RO/DI water.
I am going to move your topic over to the Fish forum as the Aquarium is actually an off-topic forum.

 

[promisetbg]

All new tanks go through various algae blooms as they stabilize. You could be feeding too much. Do you have a sump and protein skimmer? How long has your tank been set up..what size is it? How much of a bio-load and what do you have for a clean-up crew? Please post all water parameters..including ALK and Phosphates.