BBB is not the blame.It's the process&if you had a FC of 4 yesterday&you didn't make a add yesterday evening&with the hot weather.Boom there you go.Love how people want to blame BBB.If it could talk.lol
FC is pretty stable. Run pump 8 hours, FC is always between 4 and 6. I checked CYA about a week ago and it was 40-45. If anything I was still seeing a black dot at 40. Not really "blaming" BBB, just saying algee can appear if you really try to stick with it. My cc was absolutely zero yesterday, no pink at all. I did see an odd oily looking film on the water yesterday just a few areas; I assume it was wife's lotion or sunscreen. I'm sure the slamming process will bring it back!
edit: Is CYA accurate if I test with high FC (now during shocking)? I just did and shows 55, but pool is much cloudier than it was a few days ago when I checked it and got 40.
If you don't have returns that have circulation flowing along the walls, there can still be dead spots. It's probably even more of an issue with a pebble finish that isn't as smooth. Brushing a pool weekly is recommended for all pools.
If when you brushed this green dust were to grow in the bulk pool water, then that would indicate a problem with the FC/CYA ratio not being sufficiently high to kill this algae, but if that does not happen then it's likely to be that the algae took hold in areas of poor circulation in the crevices in the walls. Now, that said, one usually tries to get rid of algae almost completely in a pool so that this doesn't happen or happens much more slowly just from spores getting blown into the pool (so would get dealt with the next time you brushed). Since your green tint was on all walls, this means that algae was probably all along the walls the entire time and was never killed off completely.
If the walls were blue, then the other possibility would be something more chlorine resistant like yellow/mustard algae since yellow+blue=green, but I'd expect that to be more on the shady side of the pool.
The CYA test should be read with your back to the sun holding the tube in front of you looking straight down into it. That is strong indirect lighting which is what is ideal for the test to be most accurate. If you read it in direct sunlight, you will get a falsely low reading; if read indoors in not enough light, you'll get a falsely high reading. If it's really 55 ppm now, then 4 ppm FC would be the absolute minimum. That combined with the circulation at the walls might explain what you are seeing. To be sure, the CYA test is a difficult one and it's accuracy is officially +/- 15 though I believe that to be more of full scale (i.e. at 100) and that at lower levels and with care it's probably more like +/- 10 though that's still a significant range.
It'd be nice to know with more certainty your CYA level. On one hand you measured 40 and were possibly still seeing the dot, therefor it would have been something less than 40; and on the other hand you measured 55 with a cloudy pool - although I've read in these forums that a somewhat cloudy pool won't translate to a bad test reading cause we're talking inches of water depth in the test tube versus many feet of water depth in the pool. From reading posts over the years, CYA doesn't just jump up without an actual CYA addition which I'm assuming you haven't made.
I'm left to think your original CYA test wasn't accurate for whatever reason and you really need to maintain a higher base FC level, especially with warm water and a CYA level that's likely closer to the 55 number.
Tried cya again, right at 40. Earlier I was in the shade. Back to the sun, much easier to see the dot. My 1st test was also when pump was on low speed, could have grabbed a sample not mixed well. Pump has been on high for a few hours now, so I trust this reading much more. Will go for 16 shock, maybe 18 to be safe.
I started with 4 scoops of Zapit 73 to conserve my Clorox. Have some old I need to use up.
Often in our pool behind the ladder we get bits of green on the walls. FC stays at correct levels, no CC show up. Just green spots. I tossed a few ping pong balls in the water last year, and saw that not once did they come close to heading behind the ladder.
One more effect on testing that I've seen, but hasn't been mentioned much in the many CYA testing posts is the way the test tube is held. If you surround the tube with your hand, which is a natural way to hold it, the amount of diffuse ambient light is greatly diminished. If you hold the tube by it's top with just 2 fingers (back to the sun, waist level) you get full diffuse illumination and more repeatable results.
BBB is not no maintenance. We never said one could stop brushing their pool with this method. One would have to have significantly higher chlorine levels to force diffusion alone to be able to get into the nooks and crannies of pool surfaces faster than it would get depleted by any algae growing there.
tcat, what's your circulation like? Do you have 3 returns pointing for rotating flow and the last one points across towards a skimmer? Do you have floor drains? What's your pump runtime? Do you always run it on slow speed or do you sometimes run it on high speed and if so, how often? Do you close your pool in the winter or do you keep it operating (I suspect being in Austin you keep it operating)? When was the last time you shocked the pool? Though you wouldn't normally need to shock, the fact that you had algae on all pool walls and not just in one area means it's been there a while and just grew fast enough as the water warmed up to be able to be visible. You might consider a shock and brush cycle (i.e. SLAM) to see if you can kill it all off and then see if perhaps it takes a lot longer to come back (maybe letting you get away with less brushing, if that's a concern). Since we don't see this very often, I'm thinking the pebble surface may require more diligent brushing than smoother plaster.
4 returns, 1 with poolskim attached. I've been running on low 8 hrs per day. On low I really don't think it circulates well (barely feel water coming out). 2 main drains, I have that line closed half way to help skimming. Never run on high until now... but I think once my algae is gone I'm going to run 4 or 5 hrs on high.
Filter 7 psi on low, 28 on high. Going to clean filter after shocking.
Pool is open all year. Haven't shocked in 4 months or so. No ladders.
Thanks for the info. Yeah, maybe running on high for some time might help with circulation. Usually people run an hour or two just to get improved skimmer action, but I never thought about the circulation aspect. In my pool, my "low" that I use on my variable speed pump is 26 GPM so still has barely enough flow to keep things moving around and enough I can reasonably feel from my 3 returns, but we have solar and that's usually on at least part of the time each day and is 48 GPM which definitely feels like significant flow.
I think you're just going to have to try some different things to tweak for this problem, but the information will be useful to others once a reasonable solution is found.
On low, I would have the pump running for more than 8 hours. I would usually run 24/7 on low speed. You're not using much power on low, so you're not going to run up the electrical cost too much. For some pools, I find that keeping the FC at closer to 10 %, or even 15 %, of CYA to be helpful.
Because it adds CH to the water. And since you posted no CH readings, there's no way to know if your CH is already high or if you have room for it. You've got one of those fancy surfaces, it would be awful to get it all covered with scale.
Cal-hypo can also cause cloudiness, which might skew the first parameter in knowing you're done....is the water clear?
CH was about 290 before. I'll check it once the FC is back down to normal. I put the Zap it in a skimmer sock, water never turned more cloudy than the algae made it, actually cleared up quickly. I have my Clorox feeder set to hold FC (I believe), so I can go to work and not story to much about it.
I'm thinking a lot of the wall dust was dead algae since things cleared up so fast. I ran my Aquabot 4wd for two 3 hr cycles and it got a lot of fine dust (this thing is awesome).