question about my fantail goldfish

Question
i have a 40 gallon tank that is properly heated and filtered.  i have two large fantail goldfish, one iridescent shark (beautiful fish), a pleco, and two tetras.  All of these fish have been with me and in the same tank for 2 years.  recently the goldfish have been floating in the tank vertically, almost in a trance like state, with the head up and the tail pointing to the rocks, within a 10 seconds it seems like they snap out of it and swim around for a bit and then do it again.  i have researched swim bladder disease, but they do not have the symptoms that i found.  do you have any idea about what this could be and if i should be worried?  thank you.

Answer
Dear Kate,
Sounds like your Fantail's behavior may be due to poor water quality. Is the fantail gasping when she/he does the vertical floating? If so this could indeed be water quality related and/or be an oxygen shortage.

It's very important to remember that all goldfish are -very- messy creatures who produce a huge amount of ammonia. Large goldfish especially produce an enormous bioload on any tank. So the first thing I would do is a 50% water change and make sure the rinse the filter well (in tank water only) to remove excess organics and pollution. Make sure your filter is running smoothly also and creating enough surface agitation, an airstone or two would be great also!

You have quite a bioload in your tank and extra care should be taken to keep the water quality good. You may have to repeat these water changes and gravel vacummings several times to get things straight again. Remember to always make the replacement water equal in temperature to that of your aquarium and insure it is dechlorinated properly everytime with a good water conditioner.

Even though you've had your two Fantails for 2years. It's really best that Goldfish have their own aquarium designated to them. The reasons behind this is goldfish just produce too much waste, need a special diet and can't compete with tropicals very well, need plenty of space to themselves, and do best at a lower temperature than tropicals. What would be excellent is if your Fantails could have the 40gallon to themselves ( and maybe one more companion) and the other tropical fish like the Iridescent shark, two tetras and pleco be in another tank. If your pleco is the common plecostomus, keep in mind these fish frequently grow to be 12" inches and produce an amount of waste to match their size. Plecos should really be in a large aquarium of at least 50-75gallons for them to thrive.

Iridescent sharks also frequently grow to 12" inches if properly cared for. These are unique and beautiful fish but taking in the consideration of their potential size, a rather large aquarium would be needed to properly house these fish. Some say a 100gallon or larger is best.

I don't mean to be the bearer of bad news but I just thought I'd let you know about your iridescent shark and pleco. There is nothing really 'bad' about those two fish, just that they need special considerations to their potential large size once mature.

I really hope this helps and best of luck with the fantail!
Karen~