Newbie... <--- I'm referring to myself.. :)
I've been lurking around the boards for a few months, but had to create an account to respond to this...
I had a 20 gal that I had setup for a couple of years and only added water to it as the water evaporated. I had two goldfish a zebra danio, a giant danio, a gourami, and a couple of other fish.
When I upgraded early last year to a 55 gal I did the same thing for maintenance. I added water as it evaporated. I never did any water changes. I decided to get a few more fish and put in and noticed two or three days after I added the fish they would die. After a week all of the ten new fish I added were dead. I took the last few dead fish back to the fish store and took a sample of the water.
When they sampled the water and checked for nitrates and phosphates the water in the test tube turned BLACK, not dark blue, black.. The person at the fish store said I pretty much had my fish swimming in turpentine, and that's what killed the new fish. He said the older fish had grown accustomed to the conditions, but they'd probably be dead soon.
Since I was planning on changing out the ugly red rocks I had in the aquarium for tahitian moon sand, I went ahead and changed out all of the water and started over. By this time I knew not to wash the filter or contents so I didn't loose my bacteria colony. All that was about 6 months ago.
Since then, I now do 35%-40% water changes weekly, and now the water is still crystal clear, but my nitrate and phosphate tests are both yellow (good), and the new fish I've added are happy and alive.. I have a 5 and a 6 inch goldfish, a small angel, two catfish, a giant danio, neon tetras, and other fish (about 20 in all) they are all happy. Yes I know I'm not supposed to mix goldfish and tropical fish, but the goldfish were a present a few years ago, but the temp is 79F and they all are happy and my levels are under control.. :)
So if I were you, I'd buy nitrate and phosphate tests (you can buy them in a pack at some lfs). Buy the liquid tests, not the strips. When you test both of these don't be surprised when the water in the test tubes turns black. :) After that I'd start out with a 50% water change, then daily 30%-40% water changes until the levels are back down to normal. Your fish will thank you for it.
Last edited by cmarti
on Fri Mar 19, 2010 9:16 pm, edited 1 time in total.