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black on my fish

23 16:45:49

Question
i have a tank with four fish in,they are all fantails, one of them has got a black patch on his head, its only been there a couple of days but doesnt seem to bother him, they all seem healthy, is this something i need to worry about, please help, kind regards michelle

Answer
Good evening Michelle,

Goldfish are very messy and need a large tank with powerful filtration in order to dilute wastes. The ideal setup for your goldfishes would be a 90 gallon tank with enough filtration to turn the water over 6-8 times per hour, that's 540-720 gph total. While the "rule of thumb" for goldfishes is 20 gallons per goldfish, the bare minimum is 10 gallons per - that's to say, I hope you have *at least* a 40 gallon tank, somewhere in between 55-90 gallons ideally.

If your setup deviates too far from this, you are going to have a difficult time keeping up water quality. I would offset the messy goldfishes' waste production by performing large twice weekly water changes of 25%, or 50% weekly. Any smaller than a 55 gallon tank and I recommend 75% weekly.

Black patches are sometimes a sign of an internal bacterial infection, which can be treated with medicated food containing Metronidazole, such as this fine flake food:
http://flguppiesplus.safeshopper.com/256/cat256.htm?225

Black patches are also indicative of ammonia or nitrite exposure, so investigate that possibility. Water quality should be optimum before you medicate, since often times these external symptoms will dissipate on their own, provided you make the aquarium water quality as pristine as possible. That means NO ammonia and nitrites for sure (0 ppm) and as low a nitrate count as possible (up to 20 ppm is acceptable, the lesser the better). That is to say...

Definitely get yourself a water quality test kit if you don't have one already! I use Jungle's Quick Dip Pond Test Kit since it has all the basic tests - nitrate, nitrite, alkalinity, hardness and pH. Definitely not as accurate as a liquid test kit, but it's cheap (50 test strips for $10) I can find it at the local chain hardware store (the pond dept of Lowe's) and it lasts a long time, close to a year for me.

Read more here about goldfish diet, since diet is key to the longevity of all goldfish, but especially fancy ones with their delicate digestive systems:
http://www.wetwebmedia.com/FWSubWebIndex/gldfshmalnut.htm
http://www.kokosgoldfish.com/food.html

Just to recap:

1. Make sure water quality is up to snuff. Goldfish don't like a pH lower than neutral (7.0) and no fish whatsoever can tolerate ammonia or nitrite presence for long. Nitrates should be lower than 20 ppm, as low as possible, really.

2. Feed an adequate diet - i.e. not just flakes or pellets, since a dried foods only diet leads to problems. Goldfish are vegetarians and need a fair amount of plant material in their diet. Offer aquatic plants and/or terrestrial greens, you can read more about it at the websites I linked to.

3. If water quality, including environment (that is, an adequate sized tank to house these sizeable fishes!) has been evaluated, diet has been evaluated, and all is well, feed a medicated flake food just in case. Do not treat the water with medication, this often leads to problems when you are not sure what (or even if) there is disease present. A medicated flake food is a safe and much more effective way to deliver the medication right to the recipient.

I hope that helps! Just remember, whenever there is anything amiss, test the water, and when in doubt (even if you don't have a test kit of your own yet) do a water change. 25-50% water changes never hurt, and very often help, as long as you add the necessary dechlorinator. A bit of aquarium salt or kosher salt (non-iodized cooking salt) wouldn't hurt at a low concentration, maybe 1 teaspoon per 10 gallons, dissolved in warm water prior to adding to the aquarium.

Take care, and feel free to write again!
Nicole