Dirt and salt accumulations scratch acrylic, so flood it often with fresh water and wash it with a clean, soft cotton cloth. You can use a cleaner specifically made for cleaning acrylic or very, very mild soap but not vinegar, ammonia, chlorine, detergents or glass cleaners. If it isn't crazed internally, hazy acrylic can be polished to clarity. Do you also need to remove fine scratches or marks?