I use powder, mixed with a mag stirrer, filling a 1gal jug (the cheapest jug of water from the store, used them refilled with RODI), and dose from a 1L VOSS water bottle. Make 1 gallon at a time, refill the bottle when it's low. Takes very little space near the aquarium.
If you use the stirrer it's not much work. If you mix by hand I find it virtually impossible to get it fully mixed. Even with the stirrer I leave it running for over 10 minutes.
Stirrers are cheap and basically all the same. Extra stir bars can be bought on AliExpress very very cheap.