Mineral deposits bottom of pool (in the middle)

[aquaman]

I have adhered deposits on mineral in the middle of the pool floor. A little dirty brown too. With a mask on, I see this as raised patchy areas (as opposed to pitting).

I have a long story of our decision to use of decomposable slate as decorative material on walls above waterline. If left undisturbed after rain (winter only here in Cal) it would sit on bottom as MUD. Of course I would never let it get that bad. But center of pool is harder to reach with brush and vacuum, and honestly if someone made me vacuum regularly, I'd have to sell the house. I have had bad work months where pool cleaning and chemistry has been neglected.
Why do I think the slate is part of it? Because I have seen little flecks of it adhere to the bottom and I have had to scrape at them a bit to dislodge them! And pool filter cartridges, upon cleaning in the winter, can be very muddy water (more than your cartridges I'll wager).

The Polaris 280, no matter how I would change up its direction, would/will always choose to clean the floor on the perimeter rather than this central 10-12 feet. BUT there are paths through it like the cleaner had SOME route and frequency through the area.

Q (finally!)
If I work harder at the chemistry (direct me to the TFP page that I need to review?) and I just got a robot yesterday, is it wishful thinking that not only will I reduce further accumulation, but also dissolution is possible?
Or will the answer be using an abrasive and a dive tank, or, draining the pool and acid washing?
If the answer includes vacuuming, I'll be sad. Hopefully a robot is a reasonable replacement for vacuuming. I'll also be sad if you say "no it isn't"

 

[Texas Splash]

While an acid wash is unavoidable in some situations, we also know it can shorten the life span of plaster. So if you can reduce or eliminate the patchy areas without an acid wash, that would be idea. I would suggest you first read and bookmark our

What Are My Ideal Pool Levels?

Use our tool to find ideal chemical levels for any swimming pool. Check TFP recommended levels on pH, free chlorine, cyanuric acid, and more.

www.troublefreepool.com

page. Next, run a full set of test results with your TF-100 or Taylor K-2006C and bump them against our PoolMath APP. Pay particular attention to the last result "CSI". You want to adjust the pH, TA, and CH in such a way to maintain a slightly negative CSI of about -0.3. If your CH is already elevated due to local hard water, then the best you can do is keep the pH lower to compensate. By maintaining a lower CSI for a few months, along with frequent brushing, you "might" be able to lighten those patchy areas. No guarantee, but it's worth trying before an acid wash.

 

[aquaman]

Thanks Tex!
TF-100 used - total chlorine is good and FC good.
Answer what you have time for (?) and I can re-ask what you don't in separate posts...

1. My water currently has 475-500 ppm of Ca++ (tap is about 125) -- with the water temp and pH at 7.8 the CSI was NOT good.
2. Never really braved a lot of acid before but when calculator said TA was too high at 110 I added one gallon muriatic and aerated (hot tub pours into pool and more so when I turn on "spillway" and air blower that creates a roiling surface.
3. pH went down to 7.2 and that satisfied the CSI to the -0.3! TA reads now at 90 and pH = 7.5-ish

Qs:
I don't understand the value of chasing the TA to help control sudden pH changes when controlling the TA requires lots of pH management and electricity to de-gas the water. (does ripples on water count too?) Could you say there is another reason to manage TA.

Should I maintain the pH =7.2 to create good CSI as my main focus? At least until scale is gone?
15 yr old pool - maybe there is need for re-surfacing - don't know what that entails. Emptying pool in Cal with drought threat is always an added consideration.

Added complication: I abandoned my SWG 2 yrs ago -- It was in good shape, even bought a new one, but could never sustain chlorination without added chlorine (whole different topic). BUT have not added salt in 2 yrs (can still taste it a little). Do I need to take water to Leslie to measure salt to come up with a "fudge factor" about what test level is "good"
manual v. SWG? (should I make this a separate post?) I assume rainy Cal winters would eventually overflow the pool and continue to diminish salt? But if Ca++ is so high despite rains I guess rain dilution may be minor.

 

[mknauss]

but could never sustain chlorination without added chlorine (whole different topic).

What model Aquarite is it? You need a T15 for your pool size.

 

[aquaman]

It is a T 15 Marty. The last time I had pool person look at it the comment was made that I really should be operating it 10-12 hrs per day if I really wanted to allow it adequate time to chlorinate. That seemed excessive use of electricity.

 

[mknauss]

I would say at least 12 hours per day to generate the chlorine needed.
The next time your need a new motor for your pump it will have to be a variable speed (California and Federal Law). At that time the extended run time will be inconsequential to your electrical usage.

 

[aquaman]

I do have a variable motor. I know that when the cell was in use my chlorine need was lower but not nil. That was based on 8 hr run time. The SWG cartridge is just a pipe now, box unplugged. Will probably not initiate it. I read a lot of posts here and verifying it was operational became confusing to me (can't remember what stumped me -- had a lot to do with the box/buttons and I got conflicting information about whether measuring Cl at the output end of cartridge was valid (drips). So I unplugged it, stopped buying salt and took over with liquid chlorine.
For now my question is -- do I need to determine my falling salinity in chemistry measurements. Has been 2 yrs of no added salt and I'm sure two years of winter rains have been dilutive, (2 yrs ago - not so much last winter)

 

[mknauss]

Liquid chlorine adds salt to the water.
Salinity effects CSI some Poolmath assumes you have 1000 ppm as long as your pool set up is a chlorine pool.