What I did:
Rinsed the sand really well. I parceled it into 5lb increments (used a 20lb bag + a 5lb bag) and rinse each portion using a 4.5 gallon bucket, my kitchen sink/sprayer, warm water, and a wooden spoon. I'd spray the sand, agitate and stir it for 5 minutes, let it settle for 1 minute, then dump the water. Repeat x15-20, depending on how well it was working. Then, when done, I dumped ALL the sand back in, and then used the sprayer down into the sand (ultimately destroying my sprayer, oops), until the water was running clear.
Then, we took another 4.5G bucket, poured in 4 gallon of tank water (cycled, with perfect parameters), put in our decor, then the larger rocks (we had large round river rocks over rounded pea gravel). We removed the bubble wand and put that in the bucket. Removed our fish. I put my betta in a tannin-treated tank water kritter keeper and the others in a small filtered tank water 1.5G cube (mollies and platies and otos). The kuhli loaches were impossible to catch.
Then we removed the remaining water til we were down to maybe 4-5 gallons.
We started to remove the gravel, using our medium-sized net *hubby was helping me*. We tried to keep some of the mulm, because I had been told and read that it has BB. It started to get murky super quick and we had to be methodical about it to keep from accidentally scooping one of the two loaches (one of which is regrowing an injured fin). Eventually, we got the majority out. I wanted to leave a fine layer of gravel underneath the sand, to at least keep some of the BB.
Then we added the sand (which I had poured Stress Coat and Quick Start into, dosing per the bucket/amount of water, minus to sand weight, which I had converted and did the math on. We used a small plate to guide the sand. It was extremely murky at this point. Again, we were methodical to try and avoid hurting the loaches.
Once done with the sand, we added new water (tap water, same temp, conditioned with Seachem Prime per the instructions). It cleared a lot, but I did end up using 1 packet of the Bio-Magnet clarifier that came with the sand (Caribsea Super Naturals). It helped it clear even more, but it was definitely still pretty murky. We added the decor, replanted the plants, and I dosed it with Leaf Zone per the instructions. We let it settle for 45 minutes, I checked the prams, they were perfect, despite the cloudiness, which surprised me. Then we acclimated and returned everyone to the tank. No one acted shocked, stressed, or otherwise off at all. The mollies were very unsure of the sand though. They huddled together, swam submissively, kept investigating the gravel, etc. The platy acted like normal (always shy), and the Betta, he was just like, all right, I'm ready for bed, turn the lights off woman! (It was around 8:30 at this point, 2 hours past normal lights-out. It was total time maybe 1.5 hours of work?) I decided against feeding them, not wanting to add more possible waste at that time, plus the betta was a wee bit bloated after eating a piece of the mollies' algae wafer.
Next day, prams still clear, but pH had tanked. It went from 7.0 to 6.6. I added a very small portion of crushed coral to a bag in the filter (like, maybe a quarter-sized amount?). I know 6.6 is acceptable for everyone, but that's a big drop all of a sudden, plus, I wanted to be able to add my blackwater extract again, and that lowers the pH too.
Today, prams were still perfect, pH at 6.8-7.0 (can't tell, the colors are so similar on my chart). I added half a dose per instructions of the blackwater extract. Water is hardly murky at all now. Everyone is cool now, don't mind the sand. The loaches are much happier. The injured one has hidden, but before, with his injury, he was unable to dig into the gravel and hide, while the healthy one was. That one was MIA for a month and a half! So now he is out, rooting around like he owns the place, while the injured one I suppose is in hiding. I saw him yesterday morning, but he hid since then. Hopefully he'll heal up even better now (he was already vastly improved from the beginning of his injury).
My question is: how long can I worry about a mini-cycle? I intend to keep checking daily for 2 weeks. Is that too short/long?
Thanks! And any critique on our method is welcome. It's already been done as of now, but I'm still open to criticism, just in case we do something similar in the future.