Pool owner here...... Anyone who has maintained a pool knows that algae is a constant fight - you don't just get rid of it, it is not a "once a done" thing.
Organic material is constantly being deposited in the pool. It literally falls out of the sky - dirt, pollen, leaves/pine needles, dead bugs, bird poop. And of course, algae spores. Organic material feeds the algae.
So you constantly maintain a level of sanitizer, usually chlorine. Chlorine depletes over time, so you are constantly adding it. You also have to maintain pH. Adding chlorine causes pH to rise, so you are constantly adding muriatic acid to bring it back down. Rain lowers pH, but it's rare to get enough rain to make any significant difference.
I have a typical residential kidney shaped pool, 20K gallons. Not a big pool, about 35'x15'. It uses 2-3 gallons of 10% chlorine and 16-24 ounces of muriatic acid per week.
So to keep a pool clean and clear, you need circulation, filtration, and chemical balance. Constantly maintained.
From what I understand, the DC reflection pool has a very poor circulation system. Reports say that fixing it requires ripping a lot of the structure out to install necessary plumbing. This makes sense - if I needed to add additional drains and/or jets to my pool, it would be a major renovation. Busting up concrete, complete new plaster, etc.
Changing the color to a dark blue does cause it to retain more heat, but truthfully I think this is a marginal problem - I guarantee that the water temperature in my bright white pool on the gulf coast is a usually fair bit higher than the DC reflection pool, even with its new dark color. The stupid thing about painting the reflection pool any color at all is the fact that a proper repair calls for ripping out the bottom of the thing first, then installing adequate plumbing, pumps, filtration, and equipment to help monitor and maintain chemical balance. Then rebuild the pool structure, and include any desired color in the plaster itself. In all my experience of pool ownership, any coating applied on top of existing plaster will fail pretty quickly. Painting/coating pool plaster is nothing but a cheap/quick fix that is usually done ahead of selling the property, never lasts more than a few years. Maybe they used some kind of new high tech coating that I've never heard of, but I doubt it. If such a thing existed, the pool renovation companies that are constantly sending me ads would be pushing it. But anyway, it makes sense that a real estate swindler like Trump would think painting a pool was a great idea.
And then, when you finally refill the pool, you plan for chemical balance. All by itself, the fact that they now have a bunch of guys pouring hundreds - if not thousands - of gallons of H2O2 into the refection pool by hand, from single gallon containers, shows that these people have no idea what the f^@k they're doing. And they have no clue that this stuff has to managed constantly.
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