I'm going to preface this by saying I didn't re-read your entire thread, but I did glance over it again.
If I'm understanding correctly, you have been slamming for algae for about a week and are not understanding why the algae is not completely dead and gone yet. In the past you have used typical pool store methods and they have worked well for you, but this time it didn't work as anticipated so you are now trying a TFP SLAM Process for the first time. You are now very familiar with the SLAM article, but have made a few modifications (targeting FC above SLAM level and using Cal Hypo instead of liquid chlorine).
In my experience reading lots of these threads, there are a few things that can make a SLAM take a longer time.
- Starting with a swamp (super green water, can't see the bottom, unknown solids on the bottom, etc.) - this does not seem apply to you.
- Not brushing every surface in your pool (walls, floor, steps, etc.) at least once per day
- Not testing and adding FC often enough - the minimum is twice a day, but the process will go faster if you test 3-4 times per day. This is hard if you work, but a schedule that seems to work for most is first thing in the morning, as soon as you get home from work, after dinner, and before you go to bed.
- The CYA test was performed incorrectly (proper lighting and test method are critical) leading to a false lower CYA reading (and therefore a lower than necessary FC target)
- Algae is hiding somewhere and you just haven't found it yet... this can sometimes be a tricky one, and might be the problem you are having.
- If you have any features like a waterfall, fountains, solar, etc., make sure you are running the SLAM level FC water through them once or twice a day.
- Check you skimmer and wear door carefully for signs of algae. The wear door has nooks and crannies algae can hide in, including the tube where the foam goes to keep the top of the door floating at the surface.
- If you have a removable pool light with a niche behind it, make sure to remove the light and make sure there is no algae hiding in the niche behind it.
- I've seen once or twice that someone with an above ground, or in ground liner pool had algae on the other side of the liner that was somehow getting through... they didn't find it until they replaced their liner (I don't remember what pool surface you have but I think you mentioned vinyl liner)
Some other questions and comments specific to your situation
- Have you been noticing progress at all during your SLAM? Has there been a reduction in the amount of algae you see or an improvement in water clarity?
- Targeting slightly above your SLAM level is fine (i.e. 30, when your target is 28), but too much higher is really just a waste of money because the FC will burn off in the sun faster than it kills the algae because your CYA is no longer protecting it. The people targeting FC levels much higher than their SLAM level are usually the people complaining that they are spending excessive amounts of money on chlorine and not clearing the algae any faster. It's ok if your FC level dips a bit below SLAM target while you are at work, just bring it back up as soon as you get home.
- With the TFP method it's better if you measure your chemical additions, yes this may mean you are only using a partial bag. I use plastic measuring cups for wet and dry chemicals, other people use a kitchen scale for dry and plastic measuring cup for wet, other people approximate based on % of the container (i.e. if pool math says you need 0.5 pounds of Cal Hypo and it comes in 1 pound bags, adding about half the bag is close enough)
- Not related to your SLAM, but I believe you said you have a vinyl liner pool and do not test CH because it's not relevant to a vinyl pool. While this is partially true I do want to clarify this. For vinyl pools, there is no minimum CH, so areas with low CH in their fill water often don't test CH very often. That said, high CH levels can cause scaling problems in any pool type. Since you are using Cal Hypo as your FC source and Cal Hypo adds Calcium along with the FC, I do recommend that you test CH (Calcium Hardness) periodically to make sure it does not get too high. Testing CH once every couple weeks, or once a month is probably plenty, but you should have a general idea what it is to prevent scaling.
- I think you also mentioned your CC has been testing at 0.2 or less... This tells me that you are using the 25ml test for FC. You can save money on test chemicals and still retain plenty of accuracy by using a 10ml water sample and a single scoop of powder when testing FC/CC. Doing it this way, each drop is 0.5, so count the drops to clear then divide by 2 to get your FC level. With a target of 28 FC for your slam this will likely improve your testing accuracy since you will be using fewer drops to achieve your result (and therefore reducing testing error)
Thank you for this thorough review. Even after reading the SLAM article, all this discussion has really helped me understand all the points better. What was totally new to me was the need to test for CH and a better understanding of FC needed to SLAM, which i understood as a minimum and i thought that chlorine should not fall BELOW that number. I am still a little puzzled because my starting post said that i could not get rid of my algae although maintaining a very high FC level and i was told that if i did not SLAM i was not really killing the algae:
"You’re never really killing the algae completely, you just knock it back and then it regrows."
but later, when i said, i was keeping the FC a bit higher than recommended so it didnt slip below the target amount during the day,
i got the following advice from Donldson:
"Algae is killed at any chlorine level, SLAM is just the optimal level above which there is diminishing returns on kill rates and increased risk to liners and equipment. I'm not sure where the misconception that algae doesn't die below SLAM level came from, if that were the case we couldn't maintain clear water at normal target FC/CYA ratios..."
So, i am still a bit confused as to why the algae never dies completely if a lower FC level should work.
I will try the liquid chlorine next season and see how it goes.
Thank you everyone for your time and patience. Hoping to see with an OCLT is the algae really is dead.
One problem remains - which no one responded to is - how can i tell if i have chlorine loss overnight if i am having so much trouble getting an accurate reading:
as i said in a previous post: "I cannot see if i pass an overnight Chlorine loss test because since my chlorine is so high, when i test the same water sample in succession i get different results. i called taylor and asked what is wrong with their kit - i keep getting different results and he told me that a 10% difference is normal. So with chlorine over 30ppm, i may have a reading once of 33 and then next of 36ppm etc. So its really hard to know if i am losing a bit of chlorine overnight. But otherwise pool is clear, no combined chlorine (or .2cc) and the issue continues to be that when i brush a see a bit of yellow dust cloud into the water and i want it GONE. from past experience, if i let go for a day or two it will spread and spread..."