So here's the situation.

Had a 55 galon tank, was too big.Maitenance was too much and essentially it was a temporary thing when it was purchased anyway. Temporarily housed several( aware of size requirements, it was a temporary thing)goldfish over the winter months until pond could be fixed.

Was always well cycled. Plants thrived, fish were happy and healthy. But it was big, took up a lot of room and because I'm not very good at scaping, Kinda a cluster fuck.Ive always used a sand/ gravel mix substrate( was better for the goldfish,stopped them from sucking up the substrate while foraging), never an aqua soil based one.

Now I've downsized too a 30 gallon half cilander tall. But have been struggling to get plants too flourish in the same way they did in the 55.Fish are doing great( sorority of 4 female Bettas, a couple mollies and a few guppies, yes it's a little overstocked right now will be splitting later on to another 30 gal once this one is established, unexpectedly rescued 3 Bettas from a really shit situation,one problem at a time!)but my floaters, duckweed,giant duckweed and red roots, keep dying and my ludwigia is clearly struggling, java ferns and bamboo, both fine but no real growth in the last few months.( I think it would take a nuke too hurt those ugly things tbh) Water levels are perfect, which is weird because I thought decaying plant matter would cause a spike( so I've been removing it) and I do weekly 20-40% water changes

Tank is in a windowsill so gets natural sunlight for 4-5 hours and then artificial uv light for 2-3 hours in the evening. Have not used any fertilizer previously but did order some with the aqua soil. And will beslowly introducing that too the water changes.

So I made the decision too purchase some aqua soil and its coming tomorrow.

My second filtration system is still a couple months out though so after rescaping will have to do a largely fish in cycle, so they aren't without proper filtration for too long. Keeping filter media and some cycled water from the tank to make that easier. But I've read that aqua soil can really fudge up water levels and I'd like to know what to look out for in the following days to prevent this from being a disaster.

I plan on capping the aqua soil with the same sand and gravel mix I'm using now. I heard that can help?

Any advice on making this less stressful for the fishes is appreciated too. I've emptied part of the current tank into my 5 gal hospital tank( Rubbermaid bin) and will be putting them and the filteration in there while I work on this tomorrow an want to keep the stay in there as brief as possible.