Koi Fish Information Centre

As you already seem to know, fish will change color for a number of reasons and stress is one of them. Yes, they can and do learn to recognize people. Are you turning on a room light first or just going from darkness to the bright tank lights? I try to mimic nature by only turning on a room light at first for an hour, mimicking sunrise, to give the fish a chance to adjust to the coming daylight… when the tank’s lights are turned on. Same with turning them off at night. Turn on a room light first, then turn off the tank lights. Then an hour later, turn off the room lights.
What are the other water parameters? Ammonia, nitrite, nitrate, etc.? Did you fishless cycle the tank or are you possibly still in the middle of cycling with fish? It can take up to two months to get a tank through the nitrogen cycle… even longer if steps weren’t taken to insure that the nitrifying bacteria were not harmed during their establishment.
What kind of pH test results have you been getting? Are they staying the same each week or how much are they going down between PWC’s?
If you’ve been testing the other water parameters and the tank cycled OK, then you still need to test your nitrate levels. It’s possible that your PWC (partial water change) schedule is sufficient but without testing the nitrates on a regular basis, they could be getting higher and higher which will cause stress issues to fish.
With BIG fish, weekly (or more often) filter maintenance is also important to remove the waste. I have a long article on proper “Filter Maintenance And Cleaning” on my blog. Doing this properly, especially while the tank is still new, is very, very important as improper filter maintenance will likely result in a new mini-cycle happening each time it’s done improperly.
Further, as the fish grow, more frequent tank maintenance will be needed. For example, a 12″ Oscar is not just equal to 12 1″ Oscars… more like 1,000 1″ Oscars. I’ve never done or seen the math for Oscars but for goldfish and most other large bodied fish, they grow in body mass by eight times for each time they double their length up to around the 12″ mark… after that the escalation in body mass increases at an even faster rate. Here’s the basic math. A 2″ fish is equal to eight 1″ fish. A 4″ fish is equal to eight 2″ or 64 1″ fish. An 8″ fish is equal to 8 4″, 64 2″ or over 500 1″ fish. A 12″ fish tops the 1,000 1″ fish scale in the body mass measurement. So… the tank maintenance (PWC’s, filter maintenance, gravel vacuuming, etc.) that was done when the two fish were 2″ or 3″ would have to be more than doubled each time the fish double in size.
As you can see from the above, your 55G will need to be upgraded as well. A 55G isn’t really enough tank for even a single Oscar. The figure I’ve seen is 75G for even a single Oscar to make life a little easier on the fish and the fish keeper. Two big fish would need almost double the tank size. There is also a guideline that a tank should be at least 6X to 8X longer than the largest expected adult sized fish to give them adequate swimming room.
Lenny Vasbinder Fish Blog - http://GoldLenny.blogspot.com (Links to any articles referenced in above reply are listed on the right side, alphabetically under Labels and also under Archives by Year, Month)

Category: Philippines Internet Koi Society