I kept a fairly large pair of Red-Eared Sliders in a 75-gallon tank for many years. About a year ago the turtles were adopted by someone else and the tank has been running with a Fluval 304 all the time the tank has been empty, with no heater and with no maintenance other than topping off the water level.
Recently I decided to try, for the first time, to keep some fish. I did a 100% water change, vacuumed everything from the gravel and washed the filter and the media with tap water. Assuming all bacteria had died because of the lack of inhabitants or had been killed by the tap water cleaning, I refilled the tank and started the filter. I added a 300w heater (temp 78), an airstone, the same gravel and chunky rocks I had used with the turtles and some fake silk plants. About a week later I added three little Buenos Aires Tetras and started waiting for the tank to cycle. Ammonia and nitrite levels remained at zero for three weeks, so I assumed the three little fish were not providing enough bioload to get things moving. I added three quite small Bala ďSharksĒ and in about three days there was measurable ammonia. Within another day the ammonia was up to about 1 mg
I did a 25% water change to dilute the ammonia. Within two days, the ammonia was reading zero again. I have not yet seen any nitrites. I was using a Tetratest Laborette kit and I thought maybe I had missed the nitrite entirely. Yesterday, I bought an Aquarium Pharmaceuticals Master Kit, which clearly shows that ammonia and nitrate levels are zero. Is it likely this tank has cycled and I missed it? Or am I still waiting? I donít have a nitrate test yet.
The fish seem happy and active and are eating well. I have a pH question, but Iíll post it separately. Thanks for your responses. --Charlie