I have this goldfish with a little speck of white on its tail. There is also this faint redish-brownish thing on its tail as well. i'll have to post pictures tomorrow. Can anybody guess what it is? D:
Hi Lil' fishy. There is a parasite called Ich that's also called white spot disease that is very common with goldfish (and many other fish, of course). It's usually easy to see and something we just learn to watch for. It looks like a bright white speck or grain of sand on the body or fins of the fish. You may also notice the fish trying to scratch itself against rocks or gravel when Ich is present to get rid of that itchy sensation.
All it takes to have an Ich breakout is some form of stress.. being shipped or transferred from one tank to another, poor water quality, sudden change in temperature, overcrowding, .. the cause could be anything like that. Ich can also show up as a secondary symptom when something else is already wrong - another illness or injury.. bloat problems.. and so on. But don't worry, treatment to kill the parasites is easy.
What you want to do is get some Aquarium Salt and have a heater on hand you can set up. As a back up, it's also good to have an Ich medication you can use if the first attempt at treatment doesn't work.
If one fish has Ich, all the others in the same tank do too whether you can see signs of this in them or not. So it's best to treat the entire tank at the same time. That parasite produces tiny eggs by the thousands (too small for us to see) which end up everywhere, on the gravel/etc. Those eggs hatch quickly into free-swimming organisms which seek out a host (another fish) to continue this cycle.
The easiest way for us to treat for this is add the Aquarium Salt - check the package directions, it should be something like 2-3 tablespoons of salt for every 5 gallons of water. Dissolve the right amount of salt in some tank water first, then add it to your infested tank. Set up the heater then and slowly raise the water temperature to 86 degrees. (No faster than a degree or two per hour.) And that's it.. just leave everything this way for 10 full days. If you need to do a water change during this time, that's okay. Just maintain the same temperature and add back enough salt for the amount of water you replaced.
The salt kills the parasite only during it's free-swimming stage and the higher temperate speeds up the life-cycle going from adult > eggs > new parasites. The 10-day timeframe makes sure all the mature parasites have died off, all the eggs have already hatched, and all the free-swimmers have been killed by the salt/high temperature. After 10 days are over, let the temp come down again slowly. The salt content will be removed each time you do your regular water changes.
After this, you'll just keep an eye on them to see if these symptoms reappear. That's because there are some strains of Ich that are resistant to the heat/salt treatment. If this is the case here, then you should follow this treatment with use of Ich medication.
While your focus now is directed at erradicating the Ich problem itself, don't forget that this happened as a result of high stress. Ich is a sure sign that something else was already wrong. So you need to also determine what caused the high stressful condition in the first place and resolve that. Otherwise, this will just happen all over again.