Baldur had some orange spots on his head when my gf brought him home three weeks ago, but we thought it was just his natural color. A few days letter he lost those scales near his dorsal fin, but I read that that could be normal stress from moving. Then we went through the "Is the orange growing or is it my imagination?" phase, but pictures confirm that there's more orange than when we got him. He's also developing some magenta-colored streaks in his fins that we thought were an improvement in his color "because he's so happy and healthy", but now I'm questioning if that's Velvet, too. He seems happy, is eating well, curious and active, spreads his fins, and they're not clumped, nor is he constantly flaring.
He's currently in a 3gal aquarium that a friend gave us. It was already cycled, so seemed convenient. I added a few plants, and have a small cyano-bacteria problem, but have reduced the light period and am removing the bits I can with a turkey baster- hopefully getting that under control. Ammonia and Nitrites are constant 0ppm, Nitrates start to show up after 4ish days, and then I do a 30% water change.. I'm using RO water, because that seemed to be universally approved, and remineralizing it with Imagitarium Aquarium Salt, but following the directions on the bottle leaves my water still super soft, with GH and KH not even detectable on the strips I'm using. 50% more raises KH to 80ppm and GH to 60ppm which seems low for what most sites recommend (but different websites are all over the place), but also raises my pH to 7.5, which is higher that what I've read Bettas prefer. His previous heater was struggling to keep the tank at 75, and it was likely getting colder at night. I put in a new, bigger heater and set it for 80 - but that heater is technically too big for the tank and I'm worried about other problems. I also bought some alder cones and am going to put one in to add tannins to the water, and hopefully bring down the pH. He has a shrimp and snail friends, so copper sulfate isn't really an option right now. Is there anything else I should be doing in the short-term?
Long-term, I have bought a 6gallon tank and am going heavily-planted, but I want to make sure it's cycled properly and plants are established etc. before I move him, plus I'd rather not take the velvet along for the ride, if that's what's going on, so I'm not expecting that tank to be ready for a few weeks.