So your pool is green... don't panic. Here are two ways to clean it up in 24 hours:
Green Pool Clean Up Step by Step:
Make sure the pool can be cleared up vs draining it and refilling the pool. A rule of thumb is that if there are more than 4 inches of sediment on the bottom, a draining may be better. This would be a lot of algae and dirt on the pool bottom so more like a pool that has been sitting unattended for over a year or more. Generally, a pool that has only been green for a few months can be cleared up with just chemicals and algaecide.
Step One: Scoop out all of the leaves and debris from the bottom and surface. Don't worry about stirring everything up, you will vacuum at the end of the treatment.
Step Two: Brush the pool as best as you can. Some of the algae might be really tough to brush off. If you have a plaster or Pebble Tec Pool a Steel Algae Brush will help. But a lot of the algae will be loosened once you add the chemicals to the pool.
Step Three: If you have a D.E. Or Cartridge filter take it apart and clean it. The filter type is usually on the label on the filter.
If you have a Sand filter you will just be Backwashing it during this process. For a D.E. Or Cartridge filter, you probably will have to clean it again at least one more time or more.
Step Four: Bomb the pool out. You want to bring the chlorine level up to 30-50 ppm to start to kill the algae. A lot of the chlorine will be destroyed by the algae and other organic material in the pool in the first 24 hours. A shorthand guide:
14,000-gallon pool: 4-6 gallons of 12.5% liquid chlorine or a combination of that and 1 lb. Bags of shock.
20,000-gallon pool: 8-10 gallons of 12.5% chlorine.
30,000-gallon pool: 12-16 gallons of liquid chlorine.
Again, you want to bring the chlorine level up to Blazing High levels.
I suggest using Sodium Bromide to help kill the algae. Sodium Bromide is very effective, however, it does “use up” some of the chlorine so don't over do it. I suggest one capful added with one gallon of liquid chlorine. So if you are adding 8 gallons of liquid chlorine, 4 capfuls of Sodium Bromide should be sufficient. You want some of the chlorine to be active so you don't want to add 8 capfuls of Sodium Bromide to the pool. Each Capful is about 4 oz.
Step Five: Run the pool for 24-48 hours straight during the process. You may have to add more chlorine after 24 hours and clean the filter again. No need to vacuum the pool yet. Let everything slowly settle to the bottom first. This may take a couple of days.
Step 6: After the pool has cleared enough for you to see the bottom, you can manually vacuum out the pool. The stuff on the bottom will be dead algae and other organics like dead mosquito larvae and other bugs and plants. If you have a sand filter or a D.E. Filter with a “Waste Mode” vacuum the pool with the Multi-Port Valve to that setting. If you do not have a backwash valve with a “Waste Mode” you can vacuum directly to the filter. Note that you will need to clean the filter after vacuuming if you do not vacuum to Waste.
YELLOW OR MUSTARD ALGAE:
Any Sodium Bromide product will work effectively in treating Yellow Algae. As long as the active ingredient is Sodium Bromide it will work in clearing up the algae.
Bring the chlorine up to what we refer to as "Blazing High" if it is at zero ppm. One common mistake is not starting with a good chlorine level. Sodium Bromide will convert the chlorine to Bromine and the Sun will also burn some off as the Bromine Molecule does not bond with the Cyanuric Acid molecule (conditioner does not protect Bromine) so even more chlorine will burn off. And some of the chlorine will be "eaten" or used up by the Yellow Algae itself.
So it is very important to have a good chlorine level first 5-10 ppm and to also add a gallon of liquid chlorine or Clorox bleach with each 4 oz. capful of Sodium Bromide. Otherwise you might have an even worse problem.
But if you follow the procedure in the video below the yellow mustard algae will be destroyed and you can use a maintenance dose to prevent it from returning - about 1 oz.
per 10,000 gallons.
I use Sodium Bromide almost exclusively on my route and week to week it is the most effective way to treat algae.
Black algae can be tough to treat and get rid of as the roots extend into the plaster and even if you keep high chlorine levels in the pool the black algae can still persist. It doesn't help that the heads of the black algae also offer a protective film that keeps the chlorine from killing it.
The most effective treatment in a white plaster pool or older color plaster pool is with granular Trichlor which is the same chemical found in the 3” tablets but in granular form. A popular brand is the HASA Algi-Ban. You would aggressively brush the heads off the black algae and then sprinkle the granular Trichlor even on the pool bottom, covering as much black algae as possible. Unhook any automatic cleaner and turn the system off for 24 hours if possible. The chlorine level will be really high so no swimming for at least a week or more. By the next day the black algae should be gone. I typically use a 10 lb bucket in a large pool (20,000 gallons) with moderate to severe black algae. If you pool us smaller you can use less. Careful not to let it pool up in a pile in one area as it could stain the plaster.