With a stainless steel brush.
Green pool water is caused by algae. To remove the algae, bring the pH level of the water to 7.8, scrub the sides and bottom of the pool, shock the water with chlorine, then vacuum up all the dead algae.
You need to buy a rotating water jet to put in your pool. That will help eliminate algae and cloudy water.
No, they are usually in-ground. Many prefer fiberglass for it's lower cost, easier maintenance, and better algae control.
Get an algaecide and follow the instructions. it makes no difference what sort of pool you have.
Algae, time for chlorine. Pool supply places have a test kit (ph) & can tell you how to use & what to add-chlorine or acid.
Don'Bother with the liquid algae control it will just stain your pool, Use an apropriate amount of liquid chlorine, this will kill the algae at the same time shock your water.
Ordinary ground water? A few days can see the algae form.
If the substance you are refering to is algae and the scenery is moveable you can simply remove the algae covered items and scrub them in clean water. If you are refering to an algae slime on the substrate then you can remove it simply by syphoning it into a container for disposal. If the algae is on plants then having a few algae eating fish species like plecostomus or mollys in there will help keep it under control. Excess algae is usually caused by too much light for too long.
fungi and algae can grow together and produce substabnce called lichen, on the surface of the rocks. fungus provide algae with protection, whereas algae provide fungus with nutrients.
You must clean the inside of your fish tank regularly to remove the algae that grows there. The algae grew thick on the rocks by the beach.
If emptying and refilling is not an option I would clean out as much debris as possible so as to not clog the filter and pump. I would then shock the heck out of it.
A pressure washer.