Hello everyone, after some time thinking I decided to go ahead and get a juniper. I kept a coral reef tank beforehand and after taking it down thought that a bonsai could replace that void.
Here’s where the questions start!
1.Substrate: it appears the tree came potted with a large (75% or so) potting mix component, the rest being a top layer of larger 10-20mm red mineral stone (zeolith?)
Should I in the near future repot with a majority inorganic zeolith/pumice etc? In reef tanks we used coral rock as it was extremely porous for bacteria to reside, would using crushed coral be any benefit due to porosity? It does have the ability to adsorb/expel a lot of nutrients due to surrounding ‘equilibrium.’
2. I have access at home to ultra pure (reverse osmosis & de-ionised) water (between 0 and 1 total dissolved solids as opposed to 60-70 tds out of the tap. Is using this a good idea?
3. I have a bunch of trace elements from the coral reef days; potassium nitrate, manganese/zn etc.. Are these any use?
4. I have a solatube (sun tunnel) that at one point I grew coral under, anyone know of anyone that’s tried junipers etc. directly under these? Or would it just extend inside display time?

Thanks for any and all advice!

Junipers belong outside in any weather conditions your climate puts them through, assuming you don't live on Antartica. I wouldn't keep it inside, in a fishtank or under any kind of sun tunnels. It would probably die.

The pumice/zeolith part would probably work (my zeolith does have a white/light blue color)
Not sure on the osomosis water, I just use tap water if it doesn't rain.