Ammonia and nitrite are the two most harmful chemicals to fish. Most common aquarium fish can adapt to a wide range of water hardness and pH as well as other parameters.
Some plants are difficult to raise, but some are very easy. With hornwort, you just dump in a big bunch and watch it float while it helps the aquarium water. Here in Phoenix, the water is very hard, and the pH is high. I use the old technology under gravel filters and think they help both problems once the aquarium and plants are well established. Some of the low light, slow growing plants are also easy to grow if you use a clay based substrate supplement like laterite. Some easy plants are Java fern and Java moss, the Cryptocoryne varieties and the the Anubias family. Sorry about the Latin names that are probably not spelled correctly
Most of those plants are not available in stores, and the the people who sell on Aquabid tend to use Latin names. I sometimes use Latin names like computus crashus and hokey smokes, Bullwinkle.
Now about the fish. When you say the guppies stay near the top, I assume you don't mean they're on top gasping for air. I also assume you have an aquarium heater. And by the way, if you get a big batch of hornwort, you'll probably start seeing lots of baby guppies. As for the goldfish, I don't know much about them except they are tough little guys and they like cooler water. There are lots of fish cures on the market, and I'm sure some of them actually work. However, it's a sad fact that by the time most fish start showing significantly bad symptoms, it's already too late. Other forum members probably have different opinions, and I hope they will express them.
As for family, our two daughters are grown and have their own families. That could be what made me falsely assume they were fully raised and independent of mom and dad. Our other family member is an attack trained poodle. Her picture in a karate pose is in the Off Topic section, I think.
