I've never used Akadama , preferring domestic alternatives, so I can't comment directly. When I use slow release fertilizer I mix it into the blend at potting.
Whether you use organics (pine bark) or not, is up to you. You must take into account your species and your climate . What works in your climate will not work as well in mine.
If you mixed Osmocote into your seedling mix they should not need any attention for now, otherwise if your plants are actively growing you can begin to fertilize .
I'm in zone 10a, they are Brazilian rain trees, and Tamarinds. They began life in 50/50 potting soil vermiculite mix. Then recently I moved the strongest ones into individual 6oz training pots. 100%aka and I did not mix the time release fertilizer in the aka. I was worried it might burn the seedlings roots. Should I take the seedlings out again and repot with some akadama and time release mixed soil this time? Another alternative is just using a really weak fertilizer solution every watering. Like 50% strength of the recommended mix.
What do you think?