Q.I need an acer palmatum for a tub
My tub is 21 ins wide and 16 ins in height. I would love a maple leaf tree or whatever would suit in this container, iI want one that will not grow too high, up to four or five feet. I have looked up lots on google but I am confused at this stage. Is the bloodgood one too big. I also like the atropurpureum. But I am afraid they may be too tall. Can you recommend one that would suit.

Certified GKH Gardening Expert
You will need to buy a dwarf or semi-dwarf to stay in a container that small. Even the smallest Japanese Maples will require some root pruning when the rootball reaches the bottom and sides. Bloodgood gets up to 15 feet tall (about 5 meters) so may be too large. Shorter maples include Crimson Queen dwarf, Red Select Laceleaf, Oregon Sunset, Pixie Dwarf Red, for example.
This article will give you more information: https://www.gardeningknowhow.com/ornamental/trees/japanese-maple/japanese-maples-in-containers.htm