Sure it can be saved. The only downside is how much the staining also bothers you. Algae doesn't "deep root" and make replacing mandatory.
The only way to defeat algae is by being able to know, especially during the fight, exactly what your chemical levels are at any given time. This requires a good test kit - strips and pool stores just won't do.
Go to
TFtestkits.net and get the "Pro" kit. Yes, a bit of money, but well worth it. Articles here (
Swimming Pool Test Kits Compared) can point you at alternatives, but this is the best value, with the freshest items, that still ships pretty quickly.
Read in Pool School here about the recommended levels, and especially about the relationship between CYA and Chlorine. See the articles for more details about all the things I mention here.
The key to defeating it is to know your current CYA level, and constantly maintaining a high Cl amount based on that reading. That may mean initially testing and adding Cl as often as every few hours, to levels other test methods can't measure. It will be safe to swim in. It can take days or longer - it is never a one time "shock" and done process. Referred here as the "SLAM process". Read about the Overnight Chlorine Loss Test (OCLT), which will tell you when you are finally done. There will be lots of brushing, and cleaning of accessories (ladders, lights, etc.) along the way. And filter cleaning.
You should ONLY use liquid chlorine. You may go through a lot of it. No powders, tabs, algaecides or anything else.
Letting it stay green until spring is an option, but it will be a longer, to much longer, SLAM process as there will be so much more to get rid of.
Replacing the liner and refilling with water is also an option, but you will still need to do a SLAM afterwards, as one can never clean out every tiny nook and cranny (pipes, if nothing else) where algae may be hiding. But it likely will be a much shorter length of time. You would have to factor in the added new chems you may have to add to get back to the other recommended levels after (CH, TA, pH, etc.), cost of water, and of course the liner cost.
The key to keeping it perfect after is to monitor closely your Cl levels, and keeping them in the range needed as determined by your CYA level. Tabs and powders have their downsides as they increase CYA (or CH) constantly - so your target keeps moving higher and higher, until the only solution is to drain and refill.
