Well, one of the turquoise guppies is dying. Water parameters are good, .25 ammonia, 0nitrates, 20 nitrates, ph 7.6, high ph 7.8. I put some more sand in, and wonder if he got hit by some or if he got under the driftwood, or something. He is not swimming, but lying quietly on the bottom, but sometimes comes up half way, but soon swims for the bottom. He doesn't look sick, and he's eating. I put him in a fish net at the surface, so he could eat and he did but he's lying in the bottom of the net. I put him in the net when I saw that he was surrounded by the cats on the bottom, and they looked like vultures.
I put in more black sand, but used the upside down 20oz bottle method. Take thoroughly rinsed sand, and put it in a plastic 20 oz bottle (mine was rinsed, not washed, and I also rinsed it in some tank water). Then you invert the bottle and gently squeeze out the sand right where you want it. All the sand goes out, but and cloudy water stays in the bottle, which you invert back upright quickly, and dump out. I think I saw it on you tube or possibly here or on another aquarium site. The cats needed a deeper sand bed.
So if he goes, at least he'll be in the net and comfortable, and not gnawed at.
All the other guppies and fish are doing well. No weird behavior, no flashing, no sniping at each other. And like I said, there's no sign of injury, or sickness that I can see - no lesions, spots, or bloating.