To convert 81 liters is 21gal...right.....that should be fine-how tall or deep is it? I spawn in 10-12 inches and use lots and lots of live plants as a natural divider for the female to prevent premature egg drop. I also use lot of common snails as part of the clean up crew and for infusoria development a great first food for the fry ( you know the fry are eating infusoria from the black dots in their stomach) what fry food do you plan
Getting the female conditioned is really important to get quality eggs (I am sure you know this already)
I would move the whole spawn to the bigger tank all at the same time and remove the over aggressive ones as you see them.
Females usually pick the dominate male and they line up to spawn with him-the less dominate or more passive males sit back and stay out of his way so not to make him mad and he kicks their back-side....lol......sometimes the less dominate males will not fin out very fast/good and will maintain shorter fins...not all but some do.
As long as the brothers are never separated it may work in a 20gal-but a 55g would work better and increase your odds of success with keeping two male together...you won't know unless you try-just be ready with a back-up plan
Hey now that i have a succsessful male/ female tank im wondering how you keep two males together? Im planning like a 20 heavily planted and two males and maybe 7 or so females. Also like planting it extremly heavily planted down the middle acting a wall kinda. These males will be from my current spawn . Any advice?