Hi,
Slowly. That's the key word really.
I'm assuming your talking about fish that you've just bought from a local fish shop, am I right?
I quarantine all new stock as a matter of course and cannot recommend you do so highly enough. That includes not using the same equipment on established tanks that you do on the quarantine tank, i.e. hoses, buckets, nets etc.. I once saved an almost certain entire wipe-out of my shoal of dianema urostriatum when adding some new wild caught ones which looked healthy and were feeding fine but were harboring a very fatal disease. The new ones never made it unfortunately and at great cost. This is a particular problem especially prevalent with wild caught fish which a lot of plec's tend to be.
I've also managed to keep ich out of my systems so many times I don't care to remember. IMO this is the number 1 common problem you normally face with store bought fish. The conditions in shops coupled with fish under stress are just ideal for the parasite to spread. With this in mind my quarantine tank has a bare glass bottom which makes it so much easier to deal with ich if and when you get it as you can literally siphon the bottom to remove the cysts when they drop off the fish. Ich poses particular problems for me because of my love for loaches which are very difficult to clear of this parasite because medicating scaleless fish isn't as easy. So if you have loaches in your tank be warned, steer as far away from ich as you can possibly get.
When it comes to acclimatising the fish then just do it as you would for any other fish but slowly. Turn the lights off open the bag and roll down the top, secure it in place and add a little water at a time over a couple of hours removing some when necessary. Some set up a drip feed to do this automatically and there is a gadget available that you can just float in the top of your tank and it does it all for you. Personally I don't like either method as they tend to mix the store water with your tank water. I go to great lengths to keep them apart as best as I can even giving the outside of the bag a quick wash under the tap before floating in the tank. Give the fish a final 'shower' of tank water whilst held in a net before releasing it into the tank.
I don't feed for the first 24hours unless the fish is actively searching for food which some do as they are often deliberately kept hungry in the store. That ones a judgement call really and first food is often live food but with plecs is more likely to be courgette. Something that you know they'll love, will condition them quickly, and won't spoil the water or clog the filters if left uneaten for a few hours.
Chris.
