Yes I had one heck of a time keeping that wood on the bottom! It's out now. I hope to clear out the yellow tannin.Yeah, "softwood" is not the best. It's difficult to get it to sink, as you've seen. I had a pine(?) driftwood piece attached to slate but it wanted to be a bit buoyant even after years of off & on use.
I had granite native rock in MA & they used wells in winter. My water was very soft whether from snow melt or wells, 2-4gdh, both KH & GH, & not much iron as I recall.
Everywhere has different water. It's easiest to keep fish happy in your tap water. Many common fish are commercially bred & may not need the same water parameters of their wild progenitors. (FLA has limestone I think, source of many US commercial fish farms). You may need to use RO or rainwater for some more picky species especially if you want to breed them.
What fish do you want to keep?
I had initially wanted dwarf gourami but I realize now, thanks to your advice, that that is off the table with only a 10 gallon tank. I wanted to have a couple fish that would be relaxing to watch. Perhaps a betta? I have always loved the veiltail or fan tailed goldfish. I realize they put out a lot more waste and require more water volume.
I am self employed and do quite a bit of gardening in the summer-fall seasons. Gathering rain water is more work than I want to take on for one 10 gallon fish tank. I have access to excellent bottled spring water from the Dollar Store @ $1.00 per gallon. In summer months a 900 ft deep artesian well runs in all but the coldest months just south of the town where I work.
I think I have come to a decision. I had my heart set on gourami. Does one male dwarf gourami get lonely? That is probably a silly question. If you think he would not be happy, I would just as soon look for a beautiful fantail goldfish. He could have the 10 gallons all to himself.
One more question I would like to ask. Back 20 years ago when I had both a 55 gallon and 29 gallon in my office I was fond of the filters with the bio-wheel. Now I am hearing about the "AquaClear" . I am really curious as to what you think about these two products. I had always been impressed with the technology of the Penguin Bio-wheel.