So first of all, we have to clarify what a hydra is.

A hydra is a small animal that lives in freshwater and looks like an anemone, even though it is significantly smaller (1-2cm). Why you would to keep something as “pet“? Well, I wouldn't call this a pet, rather a very interesting animal to study, for example you can cut a hydra in multiple hundred pieces and it will just regenerate itself, so you have hundreds of clones. Apart from this, it is really cool to look at when it eats or moves.

Step 1: Where to Get Your Own Hydra

You can find hydras in nearly every water pond as long as the water temperature is below 23C over the whole year and there are some daphnias (water flees) or some rotifiers in the water which your hydra can eat. Hydras often sit on a stone or water plants and if you find one, you can soak it up with a pipet, if you are not so lucky, you can just buy it at carolina biological supply or other science suppliers.

( https://m.carolina.com/freshwater-coelenterates/hydra-living/132800.pr )

There are several hydra spicies, which have different sizes or colors, for example the hydra viridissina (green hydra) lives in symbiosis with the green chlorella algae and so it has to stay in partial shade rather than its hydra companions which like to stay in complete shadow or they will seem to dissolve or desintegrate.

Step 2: What You Need

- a pipet

- a clean, small container without even the smallest soap residue

- live food (daphnias or artemias)

- a filter

- a bit of patiene

and of course your hydra

Step 3: Get Started

Upon receival, pipet your hydra into a new container with 50% of its original medium and 50% of dechlorinated, reverse osmosis or rainwater. Let it stand dark and cool (15-20C) for about 5 days without feeding to regenerate and change the water every day. The water can after one or two days be exchanged with pure reverse osmosis or other clean water. After five days begin feeding it by pipeting the life food (2-3 small daphnias or 20-30 artemia nauplias) into the hydra container and watch it feeding. After additional two hours, when the hydra spit out the food residues, change the water. When the hydra ate enough, it will divide into two by budding.

Step 4: Notes

- Hydra like it cool and dark, or else they will die

- If a hydra won't like its water, it will lose its tentacles and then it looks like a small, brown ball. This effect can be fully reversed by giving it fresh water ( it likes) and giving it enough time to regenerate.

- artemias are more nutrious than water flees but have to be filtered and washed in fresh water or your hydras will die due to over-salinity

- artemias will sting their prey, so it will die (or paralyzed) from a toxic shock.