In my opinion most all colored plasters have variations and mottling.

We are having a similar issue with our brand new Hydrazzo . Did you get any resolution? We could use your advice . Thank you

There will be some mottling/color variations on all plaster finishes. It is more prevalent on darker finishes as more pigments are used.

Application and finishing of Hydrazzo finishes must be performed correctly.

After application, the crew will come back the following day and expose the finish with muriatic acid to bring out the aggregate and remove the creamy residue. The finish is then polished to make it smooth and further bring out the aggregate. Upon the finishing of the polishing, the pool must be filled immediately. Our preference is to truck water in.

Adding a sequestering agent during filling is necessary. Close monitoring of the water chemistry is paramount namely, calcium hardness, total alkalinity and pH. We don't address adding chlorine for almost 2 weeks, if weather conditions allow. NO SALT for 30 days also. Even waiting until the following season is even better.

Brushing the surface twice per day for 2 weeks should be done.

For any finish to give good results, it all goes to the prep work and cleaning prior to the plaster application. Weather conditions and temperatures have an impact as well. I sunny locations, my contractor will set up a tarp over the pool to protect is from the sun. After the polishing is complete and pool filled, the tarp is removed.

What is the best way to clean out any debris from the bottom of a pool after hydrazzo installation? Can I use a robot poop vacuum or will that damage the surface?

Manual vacuum using a vinyl vac head which has brushes. Hover over larger debris and allow the vacuum to suck it up.