Here's mine:
When I upgraded from a 10 gallon to a 29 gallon aquarium, I unknowingly created the perfect recipe for greenwater. I'd just read an article on the benefits of anaerobic bacteria (which hadn't mentioned any of the dangers of these bacteria). So, I was delighted to find a sand substrate labeled "inert and safe for freshwater aquariums." Of course, it turned out not to be inert, releasing uncontrolled levels of minerals into the water. I also got help from a fish store employee, who asked if I planned to keep plants in my new tank. I said yes, I had a baby tears plant that was doing well in a 5 gallon tank, that I wanted to transfer. He told me that if I had any hope of keeping any plants alive, I needed "at least 2 Watts/gallon" for a "low-light" aquarium. He also sold me a micro-nutrient fertilizer, which he advised was "all I'd ever need."
So, I created an intense-light, sparsely planted tank with tons of minerals, low CO2, and almost no iron. I kept the light on for 14 hours a day, thinking that this was necessary to keep my single plant alive. Instead, I had the worst greenwater outbreak you can imagine. Unsure of what was causing it, I tried shutting out all light to the tank, killing my plant but not affecting the algae, at all. At this point, I couldn't even see my fish, and I was getting desperate. So, I did such frequent water changes that I uncycled the tank and killed some fish (including my favorite - a 2 yr old horsefaced loach). I was finally persuaded to try an algaecide chemical that contained copper and killed off my bamboo shrimp. After all that, and still no improvement, I removed all the substrate, filtered out the sand, boiled it, and put it back in the aquarium. The green water cleared up immediately, and some of my fish actually survived.
watching your favorite fish die due stupidness is not at all fun
