6 months ago, my friend gave me her intact 3-year-old, 10 gallon tank with a high-quality filter and one plant. It also had one Siamese Algae Eater, bamboo shrimp, zebra danio and two cardinal tetras.
Over the last 6 months I've added about 5 more plants, a betta, two danios, and two tetras. However, I didn't understand how to cycle or test for cycling, so I added multiple plants in one day, and four fish in one day. (I had assumed the tank would be cycling since it was so old.)
Everything seemed fine until recently. One 3-yr-old tetra died right away, but had been looking sick before I got the tank. The other old tetra died of what looked like old age months later. Neither had visual signs of disease, their color just gradually faded. However, the 3-year-old danio got dropsy a week ago and had to be quarantined, and now two of the newer fish have white fungus on their fins.
I really want to know what I'm doing wrong! Only the old tetras and danios have died, but I'm worried about the new fish. I do a 30% water change every 2-3 weeks, and I feel like I'm slightly overfeeding. However, about a month ago a friend took care of my tank for a week and massively overfed the fish, causing a huge amount of algae growth. This was also a couple weeks before the fungus and dropsy showed up, so I think they may be linked.
Today, I moved the betta, algae eater and shrimp into a 2 gal tank and used Jungle Fungus Clear in the 10 gal. Are there any other changes I should make? How often should I change the water of a (hopefully) cycling 10 gal, and how do I know for sure if it's cycling?
Sorry for the long post, but I could really use some help!