Well I think I was right. The female swordtail was more terrified than anything else. In fact, I think her fear had been influencing the other fishes- I'd noticed that since bringing the new fishes home (few weeks now) that all the fishes lay low most of the day, only getting active in the evening when it was darker. I thought they were just still getting used to the new surroundings. They were always a bit active after the partial wc in the morning (for the sake of the female sword I thought was sick), then lay low again.
One day when I removed the gallon of tank water I needed for her salt bath, replacing w/new for the water change, everyone hid from the disturbance. Had to do something else, came back 15 min later to catch the sick fish- everyone was still acting timid. After I caught the fish and put her in the bath, all the others were swimming around the tank acting perfectly normal. So I wondered if they had been cowering all day because the sick fish made the rest of them feel afraid? Because when I took her out of the tank all of a sudden there was all kinds of activity. She was in the bath for 30 min and then another 20min readjusting- I poured portions of tank water into her bath at intervals so just over 50min total. During that time I was often walking close to the tank and the other fish didn't startle, swimming around interested in each other, like I'm not there. The moment I dipped a cup holding her back into the tank, it's like I flipped a switch. All the fishes hid low in the plants again, and if some start to venture out, they darted back out of sight when I walked by the tank. Looked to me like her illness and/or fear was making the rest of them feel scared or stressed out.
When I moved out the serpaes, the swords lay low all the rest of the day- probably frightened by all the fuss when I lifted out some plants and caught the tetras. Next morning the female swordtail was swimming about in regular intervals, looking more relaxed. Picking at stuff on the rubber base of the heater, and even came up to feed. I offered them garlic-soaked betta bits. The lamp-eyes (who don't seem to intimidate the swords) cruise around lower regions of the tank eyeing the surface, then move up swift to strike a bite and dart back down again. Swordtails are much more leisurely about it- they wait until they feel safe, then drift up, take a mouthful, drift back down.
Yesterday I did this with the new serpae trio in the tank. Serpaes have a reputation for being extra aggressive at feeding time, so I prepared extra soaked betta bits to drop in the tank- I figured they wouldn't strike at the surface for the larvae yet. It all went as usual- and yes the serpaes got very excited when food was dropped in- dashing all over the tank. They are so luminous, so much vigor and shine! But they weren't going after food. They were chasing each other, and looked like a pair was spawning again- in the bacopa/elodea thicket. Blank flared and competed, but was excluded from the spawning activity- when I squirted in a few soaked pellets he did move curiously at them but some barbs dashed in and got them first. So all the extra food I put in was on the ground, and the kuhlis absolutely stuffed themselves. Their tummies were super full- I could actually see the pinkish, round shapes of the food through the belly wall - and they lay around afterwards as if with a stomachache. Good thing next day was a day of fasting for the fishes, and a water change to clean things up. (I tested the water next morning to see if an ammonia or nitrite spike from the increased fish load, all was fine. Although one of the serapes has a bit of cloudy eye).
Not sure yet how the aggression risk will work out. I saw one of the largest male cherry barbs displaying to Blank and chasing him around the day the serpaes were introduced. Day after I saw one of the serpaes chasing a barb. So far no actual injuries. It's very hard to tell the sexes apart, but I think I currently have two males and one female. If I can, will need to get more females when I increase the school.
And now that the serpae tetras have been out of the window tank for a few days, the female swordtail is like a new fish. She isn't sick after all. She was just feeling harrassed by the serpaes, I think. She swims all around the tank now, doesn't even hide when I open the curtains on cloudy days to let more light in. I've since fed them flake, fruit flies and algae wafers- they eat them all (lamp-eyes are quicker to get the flies, though- but that's okay because the swords go after the sinking foods more readily).
Serpaes in the bigger tank are still learning how things work- I remember when I had new cherry barbs, how it took them several weeks to start following the other fishes when they flock to the top for food at the opening of the lid. They approach cautiously when the barbs are swarming after food, so don't get as much to eat right now- but I have seen one get bits of flake, and another got a fruit fly this morning (spit it out several times, finally swallowed and then dashed around flaring its fins as if excited at the taste). They do not at all seem interested in sinking foods- when everyone else is piling around a wafer the serpaes approach but keep their distance- as if just curious what all the fuss is about. So perhaps when the cherry barbs get phased out (by age) and replaced by a nice school of serpae tetras, the kuhlis will finally have plenty all the time.
Too much about fish feeding, ha.