I have a 30gl tank with12lbs liverock 2 starfish and always have alot of green and brown algae plus white dust and little treelike white stuff all over why?
Tap water can contiain nitrates and phosphates . The same thing we use to our lawn.
In small amounts it's also what corals need to eat.
Tap water may also contain compounds that kill the good bacteria we need to keep the cycle running.
Without the good bacteria and the constant addition of fertilizers the alge will continue to grow.
This is why rodi water and good water quality is important
Does the white stuff blow/brush off? Looks almost like settling detritus. For that maybe use a turkey baster to blow the rocks off and think about adding a power head or 2 to increase your flow. For the algae, without rodi water to make up your salt, you will likely have algae issues due to nutrients from your source water.
To be able to help much more than that, you will either need to get some test kits to nail down your parameters or take it to your LFS and let them test for you and post the results.
When I first started a few years ago, I used tap water to make up the initial 40 gal or so with water conditioner.
When I broke down and bought an RODI, it made a HUGE difference. I use the RO buddie with a DI cartridge. Cheap and easy.
I ran it dry and had to use tap for top off water...it sucked. Im still dealing with the algae it caused.
Definitely one of the best investments in the hobby.