Pool is clear but bottom looks spotty and dirty

[BigDave]

121oz. of 8.25% bleach should add about 5ppm FC to your 15K pool.

How much to dose depends on the measured FC level and how much you predict the pool will lose before the next FC measurement / dose.

Let's assume a 3ppm FC loss in a day and the last measurement is 3ppm FC. Three 121oz. jugs of 8.25% will add about 15ppm FC raising the FC to 18ppm. if the pool loses 3 ppm tomorrow, the remaining FC should be 15ppm - the minimum shock level. Then add a bit more than a half a jug to get back to 18ppm so the FC will be at least 15ppm the next time. NOTE - this is only an example - you'll have to put in your pool's loss rate

It's important to remember to measure - dose - measure and adjust as necessary. The more often you do this during the shock process, the better it will go.

As for the wire brush - you ultimately have to make that call. perhaps someone here will recognize your pool's surface and chime in but I have a vinyl and wouldn't go near it with a wire brush.

[rkrgk]

121oz. of 8.25% bleach should add about 5ppm FC to your 15K pool.

How much to dose depends on the measured FC level and how much you predict the pool will lose before the next FC measurement / dose.

Let's assume a 3ppm FC loss in a day and the last measurement is 3ppm FC. Three 121oz. jugs of 8.25% will add about 15ppm FC raising the FC to 18ppm. if the pool loses 3 ppm tomorrow, the remaining FC should be 15ppm - the minimum shock level. Then add a bit more than a half a jug to get back to 18ppm so the FC will be at least 15ppm the next time. NOTE - this is only an example - you'll have to put in your pool's loss rate

It's important to remember to measure - dose - measure and adjust as necessary. The more often you do this during the shock process, the better it will go.

Thanks! Yesterday, I did exactly what you said. I added 3 jugs and I analyzed the water after an hour. The data showed exactly what you said. Since I got it above 15ppm I thought that was good.

FC - 18.5 ppm
CC - 1.0

I analyzed the water again this morning and as you said, it got reduced to

FC - 13.5
CC - 0.5

Almost 5ppm loss. So I added a jug more awhile ago. And brushed the walls.

As for the wire brush - you ultimately have to make that call. perhaps someone here will recognize your pool's surface and chime in but I have a vinyl and wouldn't go near it with a wire brush.

I used the wirebrush anyway and seems like there is some improvement today (even though there is lot more to do). Probably I have a gunite surface. yeah, hope someone could confirm here

Another question, does adding bleach increase the pH, I think the pH increased to about 7.9. Or is it that the test is giving me false value at high FC level?

Also, should I add a bit more CYA ? And is CYA test values accurate at high FC level?

[BigDave]

That is good but try not to let the FC go below 15ppm.

Shock levels will give falsely high pH readings - at 7.9, I wouldn't try to move it until the shock is over and FC returns to normal. I also wouldn't move CYA until the shock is over. Some people in warm, sunny areas like to run the CYA up to 90 to reduce total FC consumption and the frequency of adding chlorine - just remember to raise the minimum FC to correspond.

The black stuff may be easier to brush away after it's dead, just try to brush it enough to keep it exposed to the shock level water.

[rkrgk]

No new information, just to update that pool is looking a bit better, may be halfway through. Already backwashed the filter couple of times (pressure increased overnight to +6) and the skimmer (fine sieve) is catching lot of live algae(green). But loosing 5+ppm of Cl overnight. I guess it might be a better to add a bit more conditioner since I have below 30ppm CYA and the sun is brutal in Phoenix. And need to order more Taylor DPD-Titrant reagent as well before it gets finished. Thats all.
I am really interested to know how people remove algae without a wire brush. Big difference for me.

[BigDave]

If you do decide to add more CYA, remember to raise the FC targets as well (for shock and regular maintenance).

[rkrgk]

I decided to wait before adding CYA since I am backwashing the filter almost every day. I put the CYA (granular) directly in skimmer and I am afraid it will all be gone when I backwash. Pool is still not looking completely clean. Its hard to remove them. And they dont seem to be turning brown at all, the algae that I catch are all the ones that I brush off from the walls and get caught in fine mesh skimmer and the filter. I was hoping that once I brush the walls a bit, algae should come off quickly and turn brown. I maintain the shock level of 15ppm all the time. The walls are a bit blackish, but the algae that get caught in the skimmer mesh is green.

[BigDave]

I don't remember if you're using the pool yet or not. Perhaps you need to move to the +shock+ column of the chart. I recall reading that black algae can be very hard to kill and digs in to the pores in the surface and hangs on tight.

A couple other thoughts:
Is it still pollen season in your area? - might explain the green stuff in skimmer.
If the pollen is over and it's green(live) algae (wich clogs filters quickly), I'd guess that there's more CYA than measured or FC is dropping too low (Phoenix sun). Either way, my suggestion would be to raise the FC level to +shock+.

[robbym70]

I am really interested to know how people remove algae without a wire brush.....

My set up is totally different than yours but when I need to scrub the walls of my vinyl pool I use a stiff nylon brush. I thought maybe switching to a stiff nylon brush might be a good alternative for you if you think the wire brush is damaging the surface of your IG pool. Couldn't hurt trying it out.

[rkrgk]

My set up is totally different than yours but when I need to scrub the walls of my vinyl pool I use a stiff nylon brush. I thought maybe switching to a stiff nylon brush might be a good alternative for you if you think the wire brush is damaging the surface of your IG pool. Couldn't hurt trying it out.

I am having a tough time removing the black algae spots even with the wire brush. I think black algae may not stick to vinyl surface as it would to a gunite surface? I have scrubbed the walls everyday for three weeks continuously while maintaining a +shock+ level of FC, I got so tired, but still there are algae spots. I think there is has to be an easy way to remove them without draining and acid wash, but I just dont know what that is. Its almost gone, and is much better now, but I would like to remove the remaining patches somehow which does not come off even with a wirbrush. I was going to try some strong algecide as my next plan.

[BigDave]

I'm sorry I can't give you a better plan, maybe some will read this who has another idea.
How's the pool surface holding up to the scrubbing? How are your numbers holding?
A couple warnings about algaecides:
Some have copper - not something most that really belongs in a pool - It can stain the pool, fingernails and blond and colored hair.
Some have ammonia which can combine with chlorine to form monochloramine ( an effective algaecide but stinky and irritating ) however a tremendous amount of chlorine will be consumed trying to overcome the ammonia and chloramines.
Some have Trade Secret - I'd never put that in my pool.