Hydrogel is also known as Water Jelly crystals or Polymer crystals.

It is a compound produced in varied shapes and size for numerous uses from gardening to kitty litter. I see no real need for orchid growers to use Hydrogel.

Hydrogel crystals absorb multiple times their weight and release it slowly. They do not decompose and can last for years.

Some commercially available potting/seedling mixes for the garden contain polymer crystals or at list the labels say so. Water Crystals are safe to use.