The pool is only winning because the CYA is too highand you let FC dip too low for too long. Right now, the FC is adequate to maintain a clear pool (barely) but not high enough to get ahead of the algae growth you have. To do that, you need to maintain a FC level of 31 for days until you have completed the SLAM process. Alternately, and what you will see advised, is to hold your nose, grit your teeth, accept the inevitable, and replace half the water to get CYA down to something manageable. At 40 CYA, you'll only need to maintain 16 FC.
You will lose a certain percentage of FC to sunlight. It's a percentage, not a fixed parts-per-million, so you'll lose twice as much to the sun if you attempt the SLAM at the high CYA level you currently have. That can add up to a whole lot of bleach!
You already posess the two most important tools: a proper test kit, and this forum. You can beat the green and end up with a sparkling pool that will be the envy of all your neighbors, especially around late August, when their pools are starting to look a little hazy.
Here's some stories to inspire you. You're actually in pretty good shape compared to a lot of people you can sort of see the vacuum head down there!
First Time Shocking with Bleach
Pretty black pool
A little encouragement for those with algae and new to BBB
Frog Filled Green Swamp to Oasis---Work in Progress!!!
Before and After Pool Pics
Before and after!
A final picture set of how well the BBB method works!
Now, in case you haven't figured out just how it happened, here's a piece of writing from last year. You'll probably relate.
We'll take a 16000 gallon pool, because that's what I have. On a fresh fill, prominent national pool chain recommends 2.5 pounds pf stabilizer per 10,000 gallons, which works out nicely to 4 pounds which brings CYA to 30.
With an average loss of 2 PPM/Day or 14 ppm/week, I'll have added 8.6 PPM/CYA if I used trichlor pucks perfectly. And they recommend a weekly "shock" of dichlor between 5 and 10 FC.... 2-3 oz per 10,000 gallons. Split the difference; I'll add 4 oz. CYA went up another .9.
So..by the end of week one, I have added 9.5 more CYA. It is now 39.5. Mimimum FC for that is 3, so I'm probably okay.
Week two, up to 49 CYA.
Week three, 58.5. Minimum FC should be 5, but they recommend 3 as ideal, so the pool looks a bit hazy. So I'll toss in a little extra dichlor "shock" to jack FC up to 10. Which adds another 6.4 CYA. Keeping count? We're up to 64.9 now.
That caught the algae just in time.. we had two weeks of good luck. A steady diet of pucks and 4 oz. "shock" each week only added another 19, up to 73.9 now.
Week 6 it started looking funky, so we "shocked"it once again. CYA is up to 99.3. But minimum FC to keep algae at bay is 8, and we're still holding things to 3, because prominent national chain's preprinted sheet shows that as ideal. So algae got a toehold and the pool has a bit of a tint. So we throw two whole bags of dichlor in which jacks it another 7.6 by the time week 7 is over, we're at 116.4, because we had pucks in the floater the whole time.
So...in 7 weeks, from 30 to 116.4. Let's say there are no more algae outbreaks because they sold me a huge bucket of phos-free and another of yellow-out monopersulfate "shock" Nothing but the pucks and the extra 4 oz of dichlor "shock" weekly. So the next 7 weeks added 66.5, which brings the total to 182.9 CYA.
Now if we didn't understand this and things looked a bit hazy, we might throw an extra puck or two in the floater every couple weeks, which will drive it over 200 easily.