While watching the goings-on in the tank today, I noticed that I have quite a few new small lifeforms in the tank. It’s a mixed bag, though. The good news is that finally it looks as though the amphipod population is rebounding. I spotted a lone amphipod scurrying around a couple of days ago and today I’ve seen many of them. 
Not in the numbers I used to see them (eg swarming all over the place), but considering that the population dropped off sharply and I can go for days or weeks without seeing any, it was sheer delight watching them foraging today. 
The population decline remains a mystery. Here are what I figure are the potential reasons: low Ph (which was corrected recently), general water quality (I’m doing more frequent water changes and not feeding the tank any more), a decline in the population of predators (either that prey on amphipods or their larvae). I don’t think the predator hypothesis holds up. Though I’ve now got one less featherduster feeding on pelagic microfauna, the amphipod population didn’t Immediately decline when the featherdusters were added and the bristleworm population (which I thought might be preying on them or their larvae) has also boomed (more on that in a minute). As for water quality: well, they eat bacteria and algae and though the water quality isn’t bad I have plenty of that. I’m leaning toward the “ph theory” because while the water quality has been gradually improving with each water change, the amphipod population hasn’t until now. OTOH, within less than a week of correcting the Ph the amphipods are again out in obvious quantity.
Now about that bristleworm population. (Sigh) I noticed two small, thin, white worms on the back glass this morning. One was about a 1/2 inch long and the other about 3/4ths of an inch. They were much thinner than bristleworms, but thicker than the thickness of a hair. Say, maybe twice the diameter of a hair. I looked at them with a magnifying glass and could see no bristles. I tried to get a picture, but couldn’t focus in the tight space behind the tank. One went into the Tonga rock and the other into the substrate. Just a couple of minutes later I see a third behind the palace rock. Also white, about the same size. So, I’m wondering if this is some new worm that came in on the new rock. (If so, so much for quanratine; they’re the same color as the rock—I’d never see them!) I also wondered if it could be featherduster larvae; perhaps Elle and Belle did the spawning thing some night after I went to bed but before Elle dropped her crown. But, no such luck. 
I spotted another one (that makes 4 babies that I know of) on the front glass a little while ago. This one is about 3/4 of an inch, maybe a little more and though with the naked eye it appeared white, when I took a pic of it, clearly it was one of the grey-red bristle worms! A baby. The pic isn’t great but it’s the first one I’ve taken where you can clearly seen the worm’s mouthparts.
So, now I’ve got at least 6 small(ish) bristleworms in the tank. I’ve read that bristleworm populations tend to be self-limiting in aquariums. I’m not exactly happy that my tank has enough microfauna to support an increase in bristleworms. I’d rather the featherdusters and amphipods consume the microfauna, but they do probably get at bits under the substrate that the amphipods (maybe) can’t get at.
I’ve seen the two adult bristleworms today in different parts of the tank. I can only assume that since this population explosion today coincides with the return of amphipods in more numbers, that the worms aren’t preying on the amphipods. (crossed fingers)
To return to the subject of amphipods: I topped off the quarantine tank this morning with a little superbuffered water. I hadn’t been tending it since taking the rock out of it. I even had the pump off yesterday. I spotted tiny amphipods in the tank today so I’ve got aeration back on again. I just hope I didn’t kill them off with my futzing around with the water. They look so fragile, definitely not full grown. I’d been looking for them ever since a dead amphipod turned up in the tank with the rock, but even after removing the rock I still saw nothing moving in the debris. Then today a few turned up on the glass. I enjoy watching amphipods so much that I’ve considered trying to catch one or two (a daunting task considering the diminished numbers until now) and setting up a picoreef just as a habitat for amphipods, with the idea of reintroducing them to the main tank. Even though they look like they may be rebounding in the aquarium I still may do this, as a hedge against some future disaster decimating the population. They are good little workers and quite cute.
