I have 2 jack Dempsey they will be moving into their new 125 gal once it is set up, What are some good tankmates? Also has anyone had plants with them? Im going with sand for the substrate if that matters.
They can dig a good bit. I wouldn't personally plant anything expensive if you must go with real plants.
Tank mates:
GT
Sev
Mayan
Carpinte
possibly a RT, but I'd be super careful
A. Lyonsi
Sajicas
Con's
Aceras
pantostictus
Thorichthys Passiones
Firemouth
Salvini
Some sort of Synspilum
HRP
Bocourti
That should get you started in researching possible tank mates.
make sure to research any of those before going with them to make sure you know what you are getting into. Some may get nasty and need seperated. Some of those get pretty big, and a lot of times it depends on the personality of the individual fish (GT being a prime example as some are babys, and some will kill everything).
A lot of people keep them with oscars as well. Just make sure you have plenty of hides and break up the sight lines to help with aggression (because it's more likely than not that you will w/two JD's that get new tankmates).
I have a jack dempsey in my 90gal with a couple senegal bichirs, a delhezi & soon a palmas poll; as well as a leopard ctenopoma, pictus cat, black ghost & african brown knife. He doesn't bother anything.
He only digs out certain spots (usually just one spot) in the tank where he claims territory, usually under a cave I've built for him. So most of my plants go unbothered. Between all of my fish I occasionally get a stem plant uprooted, but nothing major.
Best to get tank mates for them when all are small so they grow out together.
This way, you don't go putting a fish into a tank where others have already established territories.
The quicker you get your other fish in there with the JD's, the better. But don't skimp on researching what you are getting first. Would not be good if you didn't know any better and got a dovii or something like that.