The tile installer used Tec Sanded Grout--Polymer enhanced prtland cement grout. He said the sealer is already in it so no need to seal the grout after. Is this correct. It is in the shower on the floor and walls

If he used Tec XL it does claim to have a built in stain blocker. That does not mean you can't still seal it if you want more protection.

Uh Oh! How long were you told to not use this shower? It's not XL grout, it's the XT grout. Actually, Tec has 2 portland cement grouts, Accucolor which is their basic polymer modified grout and Accucolor XT, which is their designer, high tech, very inherently stain resistant grout. Allowed to cure properly, Acucolor XT offers an outstanding warranty against water based stains.

Tec does not make the entire color pallet of the accucolor grouts in the XT series also, but there is a product made by their parent company (HB Fuller) called "Grout Boost" that when used with any regular grout in place of water, gives it not only the same water based stain resistance of the XT series of grouts, but also protects against oil based stains.

You need to find out ASAP what grout was used because Accucolor XT or any grout mixed with grout boost needs to be allowed to cure for 10 days before being exposed to water in order for it to develop it's maximum stain resistance.

If it was Accuculor XT, if you wish to apply a sealer, you must use a solvent based sealer after 10 days of cure time. If it was any grout mixed with grout boost, do not use a sealer.

If you might have been thinking the sealer would be needed for water proofing, sealers are designed to allow water to pass through.

Hope it all works out for you :)