In a 45g you might be better off going with one or a few of the smaller varieties of pleco instead of a datnoid, just my honest thought.
Datnoids grow fairly slow relative to fish like large SA/CA cichlids so you could keep it in a 45g longer than say something like an oscar, motaguense, midas, etc. though in my experiences having worked in the industry in the past I've noticed a lot of people unintentionally keep fish that grow slower in less than adequate sized tanks for too long because they feel more comfortable knowing the fish grows slow so it should be less likely any stunting can occur. This isn't necessarily the case when you go from theory to practice.
I don't want to discourage you as Datnoids are far and away my favorite fish and encourage anyone to take an interest in them so long as they have an adequate set up or very sure plan for the longterm housing of that/those fish.
Something a lot of people don't seem to realize and I believe it's because Datnoids are a bit more of a niche fish, is that they're literally all wild caught (ST possibly excluded now but most of us don't have $2-5k to drop on a juvenile ST) though that's an entirely different conversation.
Natural breeding seems to have been largely slowed and possibly completely halted due to damming and overfishing in their natural habitats. Until more clear evidence comes out that other datnoid populations aren't heading a similar direction to ST I would advise anyone who wants one get one and commit to keeping it for life. These fish seem to get passed around a lot, at least in California seemingly because they grow slow and don't keep up with fish they're housed with, people tire of the unstable coloring IT and some other datnoids show, not super active behavior, frequent hiding and so on and I think it's why a lot of the people I've seen here and IRL over the last 10 years don't have big datnoids, they move off them and often times the end up in the care of people who can't properly house them long term.
Sorry for the bit of a rant there, I understand this can be said for many of the larger species we keep but when fish are exclusively wild caught in diminishing populated ecosystems we should reevaluate if we should get one right now and instead find one of the many great alternatives out there that often get overlooked.
One suggestion I could make would be a nandus nandus. It's another perch-like fish with fairly similar stripping and a very similar body shape to datnoids and only reach approx 7"-8" on the high end and don't tend to grow especially fast. They share several behavioral traits to datnoids such as being ambush predators and liking to spend time under covered territory like large pieces of wood, they're typically somewhat readily available if you ask your LFS to order one and if I recall don't usually exceed $15-$20 so price isn't a particularly big issue for most and it would be able to spend a considerable amount of time in your 45g, potentially life depending on your tanks footprint and it would give you an idea if datnoids are really a fish you would like to pursue when you have a larger set up (125g bare minimum in my mind) in place.
I hope that didn't come off like I was being a jerk but I feel giving a more detailed response helps you and anyone else who reads this in the future a broader perspective on datnoids.
