This is going to be a long post, but I've been at it for a long time. I thank any and all in advance for any help they can give.
I have some algae/stain problems. I'm not sure which they are so I'll post information and photos and hopefully someone will have experienced one of these and resolved it. I've posted photos of all.
First my values: cya:40, fc:3, cc:1, ch:300, ta:70, ph:7.0
My fc, ta and ph were adjusted downward for the Jacks Magic tests mentioned below. Normally, I'll keep fc around 4, ta has been 90-100 and ph ~7.4
I have what looks to me because of characteristics, like 3 different issues:
First I have 4 spots of what looks like a vague smudge of black. There's no real definition to the shapes. They are dark in color, but not intensely dark, they don't jump out at you.
I think these are stains. I did 4 Jack's Magic tests on these with no change. I have also used vitamin C with no change.
Second, I have many spots that I think are exclusively in the spa that are darker and more pronounced. They have a linear and somewhat curved shape - like a parenthesis ")". These all seem to curve in the same form as the curvature of the spa.
Some have a dark spot about 1/8" in diameter and lighter gray extending away from it with the longest mark measuring about 3". Many are very small 1/8" to 1/2" but they're all over the spa, mainly on the horizontal surfaces, but there are also a few similar marks on vertical surfaces. I think these are an organic growth of unknown type. Rubbing on them with a white cloth yields no color residue. I scraped one with the point/blade of a steak knife, again with no residue. I did remove one of these spots using Muriatic acid - see below. I did the Jacks Magic tests on 4 of these corresponding to the 4 tests in the kit with no change at all. Yes I calibrated my water to be within the JM parameters.
Third, I have round gray spots the biggest about the size of a nickel spreading throughout the pool itself, but not in the spa that I can see. They are in the shallow and deep ends. I first noticed them on the sunny side (north wall) of the pool, but they have now shown up on all sides as well as the floor of the pool - deep and shallow. I have no clue what these may be. They are unresponsive to hyper-chlorination and brushing. They do not lighten or give off gray residue when brushed. They are individual spots rather than say a colony of spots. I haven't done much with these other than super-chlorination, algaecide and brushing since they are more difficult to reach.
I own and use a TF-100 test kit for the past 2 years (since these problems started). I have generally kept my recommended levels throughout the past 1 1/2 years while I have been dealing with this - other than when super chlorinating - though there have been a few times when the fc has dipped too low.
I have maintained super-chlorination at or above shock level for up to 3 weeks at a time, brushing x2 per day. I can segregate my spa from the pool using the valves. I have had my FC in the spa up to 50 for 3 or 4 days, scrubbing x2 per day and had 0 positive results of either elimination or even change.
I have put vitamin C on the smudge spots with no change.
I drained the spa, used a chlorine 'puck' and covered every curved mark with the chlorine and then kept the chlorine moist by hose spray for 2 days.
I have scrubbed the spa marks and applied concentrated algaecide (see Shotglass method photos) and straight bleach on them to no avail.
I've used Leslies 'black algae algaecide' in the pool while super-chlorinating and scrubbing.
I've used Poly 60 algaecide while super chlorinating and scrubbing.
I've had my water tested for metals and it shows a .6 level of copper and a similarly low number for phosphates. I do have something purported to remove the copper and will treat with that after next week, though I don't believe a low level of copper is complicit in these many problems.
The only thing that did anything is the following:
I made a 50% mixture of Muriatic acid. I selected one spot of the curved algae (?) on the top step of the spa. I drizzled the mixture onto it and scrubbed, waited a few minutes and did it again, a few minutes later again, for about 15 minutes. This did eliminate the one spot that I chose. This is why I believe it's algae.
I have owned and maintained this pool for 20 years and never had anything similar occur.
I had the pool replastered in October 2008. Put in a new heater a couple years before that.
City water. The rest of my pool specs are at the end of this post.