The other thing to realize about feeders is that they may have been really abused via crowding and chilling. They also have been exposed to all of the common fish diseases. They really, really need to be treated for parasites while in quarantine. Otherwise they will take their problems straight to the fish in the aquarium.

There are some livebearers (northern swords, some really plain Poeciliopsis, a mollie or two and some of the inland Goodieds that come from high pH waters. They are also probably more sensitive to ammonia than guppies. With pollution, there are fewer and fewer of these fish in the wild, in part because of that.

I too still need to work harder on water changes. The tanks with the healthiest fish are those with good plant growth 9and good lighting) and I think it is because of their ability to take ammonia straight out of the water column. Because those are fairly attractive tanks, they also get a little more maintainance attention.

If you have just a couple of fish, be careful that you aren't over feeding them. Feeding modest poulations really may mean watching to see that they have gobbled up everything offer in 60 to 120 seconds.

Don't get any more fish until those two seem well established. An ammonia kit may run $6-8. One for ammonia, nitrites and nitrates would run more, but less per test. High reading for any of those may accompany declines in fish vigor. Maybe something could be worked out with "Santa." ;)