There are several good items to use to clear plants of hitchhikers but they all have the same fault. Whether you use peroxide, bleach or alum, they all have some risk involved. Since they are all chemical that react with the hydra, they also tend to react with the plants. Too little reaction and the hydra survive, too much and the plant dies!
So it is not simply a matter of choosing which to use but also HOW to do the job. How strong and how long?
And that is never going to come down to an honest answer as it will vary even within the same group of plants as certainly from one type plant to another. I rarely bother to dip plants to kill things like hydra but do it more often to knock down algae so I just do a very quick, light hit with bleach as it is the one item that I keep on the shelf and handy for tank use.
But since chlorine is one of the stronger items we might use, I go for just a small amount like a tablespoon in a gallon or two and then go this way:
One bucket for dipping, one for rinsing and one with dechlor, if I plan to put the plants with fish right then. In and out of the bleach dip, without even a two second pause, then immediately to the rinse and from there to the dechlor bucket for final.
The thing I keep in mind is that there is no perfect way to kill things that will not also risk damage to the plant if it is a tender type. So that leaves me to balance what I might expect to come out of the plant that I would not want versus the damage I may do to the plant in the dip. It all requires a balance. If the choice is to dip a plant and possibly save it or throw the thing out, I go for the dip. But if it is something like Java fern which almost cries out that it will be ruined, I may throw it out and not bother at all.
You gotta kill a few to understand what to do with the rest!
Thanks for the detailed post, I agree there isn't a "one size fits all" fix for keeping pests out.
That said, I'm not too concerned over algae or snails for that matter, mostly the hydra, I think if I buy from this seller again I will make up a small 1 gallon dip treatment with a high dose of fenbendazole (I bought extra), that should take the hydra out and maybe some snails, I could probably rinse and use something specifically for snails if I'm really worried about them. Another reason I'll always recommend TC plants if you can get the species you're after.
If I get real worried I could set up a quarantine system... Plastic container and a 23w CFL bulb should do, add an airstone too.
Quarantine tanks aren't just for fish! Remove the fishy hosts and many diseases and parasites won't survive long. I've been quarantining my plants in spare tanks or plastic totes for quite a while now. You can use more aggressive solutions in a quarantine tank or bucket than you would your display tank when you do find an unwelcome hitchhiker. And you will find them.
I have had success with Fenbendazole for hydra and planaria, but there's a few other treatments folks have suggested here I might have to try in the future.
Tissue culture seems nice, but I think everyone can do just fine with the regular stock by taking some precautions.
This tank is a shrimp tank, impossible to remove them all. plus fenbendazole doesn't harm shrimp if used correctly.
As for removing fish, the diseases and parasites live on/in the fish so... removing them from the display tank wont do anything, unless you put them in a hospital tank and treat accordingly, but that leaves the display tank with possible spores/surviving parasites etc. I think preventative measures such as dipping plants/quarantining/TC plants/reputable sellers is a far better approach than "I'll deal with it when it shows up".
I should note that I am upgrading this tank, so I'm looking to treat it and then dip plants as an extra precautionary step before transferring plants to the new tank.