Yellow Out has it's uses, but is usually much more trouble than it is worth. It's big advantage is that it works even with very high CYA levels. The main problem with it is that it can create a huge short term chlorine demand, which you need to keep up with or you will just get algae again right away.
If your CYA level is reasonable you should avoid Yellow Out. If your CYA level is very high you should lower your CYA level. If lowering your very high CYA level is out of the question, then you might want to consider Yellow Out.
Yellow out is an ammonia based product. When you raise your pH to 8.0, add the product, and then shock the pool you form monochloramine, which is very effective at killing algae. Monochloramine is a nitrogen containing compound so the algae eats it as a food source and the chlorine content kills it. The problem is that after using a product like this you will find that you have no FC and all CC (that the monochloramine). It will take a few days to a week of sunlight and shocking to get rid of the monochloramine and have a FC reading but it does speed up the killing of the algae. I might speed the process of clearing a really green swamp but if your water is just a little green it's probably not worth it. IF you have mustard algae it might be useful, however, since mustard is hard to kill with straight chlorine.
The main caution I would give is to NOT overdose or the FC will be very difficult to recover. Once you treat just keep shocking with chlorine after and do not use a second dose.
Our pool was green and it seemed it wasnâ€™t clearing up after a lot of liquid chlorine/brushing. My pool store man recommended â€œYellow Outâ€ and I used it with more liquid chlorine (CYA is 40, raised PH to 8). It cleared the green out and left a lot dead algae in one night and a lot of suspended stuff in the water. I flocked it the other day and gave it a good vac to waste but it is still cloudy.
I am to floc it again and vac. to waste, but this time I will have the pool water high enough to do the whole pool. I have the socks on the filter baskets and my filter is the zeobrite sand. Sometimes I put some DE in the skimmer by hand but I have been back flushing frequently lately. But the filtere does not seem to filter dead algae.