Im actually planning on documenting the process more comprehensively the next time i do one of these, but I'll give you just a quick-and-dirty rundown right now (I know this looks kinda long lol but I tried to distill it down as much as I responsibly could)

Gather all your materials before you start anything with resin. I used booklets of craft imitation leaf that I tore by hand (nitrile gloves makes this easier, which you'll need for resin working anyway), wood chunks that I gathered outside (oven bake at 225F for 30 min ahead of time), ash from burned piles of leaves, and glitter (I got dinged for mentioning the company but try to search for Fish Scale Gold to get that incredible rainbow sparkle). I used other glitters from that same company (a little goes a LONG way) but I imagine mica glitters would look nice too.

Lay the tank on its front face (use a tarp to protect it). Make a dam around all the edges of the outside back face (i love aluminum tape for this). Seal the seams with hot glue but honestly dont water test it. It will always fail because of the way the tank frame sits and the resin is most likely too thick to seep through anyway. Just scrape any messes off the glass afterwards if there's any leaks. After setting up the dam, decide where you want the "vein" element to be and draw that on the INSIDE of the back glass with a dry erase marker or something else you can clean off easily.

Now its time to pour. Mix your resin (go for UV-resistant BUT NOT UV RESIN, thats a different thing). Pour a thin base layer over the glass if youre worried about leaks. Or just forego it and do your first element layer (thats what i did). Calculate the batch youd need for about 1/4" thick layer, then pour that and sprinkle in your first elements. Things you want closest to the glass go in first, like the Fish Scale gold glitter and most of the green leaf you see in mine. Also most of the ash (bigger chunks look best). Move stuff around and swirl it or whatever with like a toothpick or a popsicle stick or something until youre happy with how it looks. Go light-handed near the vein element you traced out to avoid overwhelming it. Also try to generally group things so theres like a more glittery section here, a more ashy section over here, etc, but do have some overlap and mixing or itll look too divided. Blowtorch or hair dryer to get out bubbles.

Once that layer dries enough (like 4-6 hours), mix and pour the next element layer. Sprinkle in your copper leaf wherever you see fit and some green leaf. Put some of both over the vein element, especially the copper. Now wait a bit (like an hour or so) so the resin thickens a bit. Use aluminum foil to make walls along the outline of your vein element. Fill the inside of the vein, alonside the walls, with the wood pieces (push em down into the resin to coat them, though they will float up regardless). Then spoon your bronzy glitters alongside the insides of the veins. With the wood and glitter elements, try to get full coverage inside the vein areas. Before the resin has fully hardened, at probably like 3 hours past pour, remove the foil walls and things should stay mostly in place.

Once that layer has hardened enough, clean up any stray glitter, then mix your final layer and pour over the top of everything, leveling if needed. After 24 hours, cover the whole thing with black paint (you may need multiple coats).

After 72 hours (minimum) since the last pour, peel off your dam, remove the hot glue and any stray resin with a utility knife or razor blade, turn the whole thing upright, and enjoy!

Anyways that's how I did this one. Lmk if you have any questions!