I believe if you check with pebble tech they will say never.
What people refer to as pebble tech is not always the same, to be on the safe side go to the following link.
http://en.allexperts.com/q/Swimming-Pool-Spa-2261/sand-blasting-tile.htm
Pool had been resurfaced 4 years ago, should it need an acid wash or was it improperly maintaned.
Yes, but don't overdo it, judge how much you need to get the job done and rinse properly as soon as possible
Hire a high presure sprayer.
Muratic acid or Sulfaric acid
add acid
Yes there should be no problem with that.
The pH level of a pool can be lowered by using a specific acid that is sold at pool supply stores. The acid is called muriatic acid, and it should be added to the pool while the water is circulating. About 1/4 gallon of the muriatic should be added per .1 part per million the pH needs to be lowered.
pool acid is made up of muriatic or hydrochloric acid that is it.
You should test your pool weekly at the very least and if there has been lots of rain or after a pool party. Liquid testing kits, strip testers, and digital testing kits are the main ways to test your pool water. You should test for total and free chlorine, pH, alkalinity, cyanuric acid, calcium hardness, phosphates, copper, and salt if you have a saltwater pool.
NO! You do not want to use Sulfuric Acid in a pool. That is battery acid and will burn you on contact. If is splashes back into your face or eyes you will be disfigured for life.=Use the products recommedede by the pool store in your area. I say this because not all areas require the same treatment.=
liquid pool acid is Muriatic acid or more commonly know as Hydrochloric acid (HCl)
If you are talking about acid washing an empty pool then yes you should be inside it to do it properly. It is best to hire someone who has done at least 50 acid washes. I have replastered many pools that were acid washed by an idiot or the pool owner because they simply didn't know what they were doing.
Run the filter when adding any chemical to the pool. It needs to circulate to do its job.
Assuming no other complaints you would only need to change water to lower the total dissolved solids level or cyanuric acid level. TDS should be below 500ppm and cyanuric acid ~50 ppm.
How much acid and chlorine should be added to a 5000 liter to make 5 ppm solution