Thoughts on why this is raising / sinking?

[TDTPool]

In one pic you'll see this issue I have with part of the concrete sinking, and the coping around the skimmer lid is also sinking. This has been pretty drastic over the last 2 months.
I'm thinking it's due to water getting under it, but curious on thoughts? I've reached out to a couple hardscape companies.

Trying to see what is easily fixable/simple, vs expensive/risky to repair of the issues I'm having. Our new pool quote came in at 170K with removing a lot of the things we want, but pretty concerned about this sinking.
You'll notice in this pic (ignore the algae issue, it's resolved) the sealant is completely folded over, so I'm thinking replacing/repairing the coping is the answer?

If it is, is this something I can reasonably DIY? It seems fairly simple to replace with pavers, just time-consuming.

 

[Bperry]

In one pic you'll see this issue I have with part of the concrete sinking, and the coping around the skimmer lid is also sinking. This has been pretty drastic over the last 2 months.
I'm thinking it's due to water getting under it, but curious on thoughts? I've reached out to a couple hardscape companies.

Trying to see what is easily fixable/simple, vs expensive/risky to repair of the issues I'm having. Our new pool quote came in at 170K with removing a lot of the things we want, but pretty concerned about this sinking.
You'll notice in this pic (ignore the algae issue, it's resolved) the sealant is completely folded over, so I'm thinking replacing/repairing the coping is the answer?

If it is, is this something I can reasonably DIY? It seems fairly simple to replace with pavers, just time-consuming.
View attachment 530277

Concrete wasn’t compacted very well before pouring the deck or water has been leaking under it.

It’s really hard to ignore that algae…

 

[PoolStored]

It’s really hard to ignore that algae…

(ignore the algae issue, it's resolved)

I agree...tough to ignore...

 

[YippeeSkippy]

I've never seen algae that looked like that before!?

 

[duraleigh]

The settling is almost surely from the concrete deck settling and not an issue with the coping. Poor compaction of the fill from underneath the decking. The solution to that is no easy task.
A "patch" fix would be to fill the crack where coping and concrete meet with a polyurethane caulk. The problem is I fear the settling will continue over time and reopen the crack. A more permanent option would be to raise the decking by pumping concrete under the decking and hope it settles no further.........that's hard to predict.

A permanent solution is to entirely remove the decking and then compact the sub base and pour new concrete..........big task $$$$

(glad you got the algae fixed but I don't think it was algae........keep chlorine in your pool)

 

[YippeeSkippy]

(glad you got the algae fixed but I don't think it was algae........keep chlorine in your pool)

It looks like one huge petri dish.

 

[Newdude]

I've seen less scuz with Baqua conversions. Come to think of it..........

 

[Bill1974]

No easy fix for the raising / sinking concrete. Is this something new? If so I would say you may have a leaking line. I am guessing your soil is of an expansive type (swells when it gets wet and shrinks when it drys). The soil is okay to use as long as the moisture level does not change or not change quickly or non-uniformly.

To fix it, the decking will need to be demoed, soil replaced with fill that does not swell and is can be compacted.

For the areas that have settled, concrete jacking or foam jacking may work, but it's may only be a bandaid.

If this is new and it was fine for years, what has changed recently? landscaping, gutters, downspouts, irrigation, etc