No. Salt water will not change or ruin your acrylic nails.
The sand of the beach might scratch you nails a bit but according to some experts, with a miracle block from EzFlow (Pro Shiner) or IBD (quick Shiner) you will get that shine back right away.
Avoid using EzFlow UV30 as a topcoat over your acrylics as you will have a problem with sunscreen oil. The UV30 will turn gummy from it and discolor as well. You may use Intense seal (IBD) or Finish It (EzFlow) to seal your nails with a gel sealer.
Are you taking good care of your nails? Here's what you need to know to keep your fingernails in tiptop shape shared by Mayoclinic.org.