Hi there, this time I"m doing my neighbour's betta tank that needs a serious do-over. Before today, my neighbours had bought a betta along with a 3 gal(I think), some turquoise substrate, and a glass tube with a cactus decoration, and the filter for the main tank. Now, when my neighbours first showed us the tank, I was but still a fish noob, and knew not of the perils of keeping a betta in a blank tank. Later, they went away, and it died. As we were still unknowledgeable, we just bought a veitail betta for 9.99. Turns out the daughter of the neighbours was taking the fish out every now and then to "play" in the glass tube. Now, even thought I was a noob, I knew this was bad, so I then told them they should put the cactus thing into the main tank, and retire the glass tube. Fast forward to today, and I've decided to snip off some ludwigias from my tank and collect driftwood and rocks. I then proceeded to take out the cactus, and place the rocks in. At this point he's stressed and hiding behind the filter, so I found the light and put it on, then walked away. Normally I would just leave it like this, and maybe add more ludwigias. However, I like my terrariums/tanks looking nice, so I'm wondering what the best way to replace the substrate is without completely disrupting the cycle. Also, she's paying me $10 a day for a week for this, so I can afford a few plants and maybe a few otos or shrimp(probably steal babies from my tank ).