The crushed coral is raising GH. Remove it. If you want to raise KH, use K2CO3. That said, there’s no reason to raise it unless you have certain fish that need a higher pH.
The pH of this tank was as low as 4.9
It will help all the plants. There’s some amazing journals recently with a few guys using low temperature to grow CO2 required plants without CO2. Amazing stuff really, drop to 74 and see what happens. I dropped my tank to 74 recently. Wish I could go lower and may just see what happens if I go to 72. Cautiously though!
Swords are just hogs for nutrients, they don’t care where it comes from. People mistake large root systems for root/ heavy root feeders. The larger root systems are for anchoring mostly. Usually from seasonal flood areas or faster than normal flowing rivers and such.
Here’s a good little blog post
https://www.2hraquarist.com/blogs/fertilize-planted-tank/root-or-water-dosing?_pos=2&_psq=root feeder&_ss=e&_v=1.0