my fish has ich

Question
I've had my fish, oh I dunno exactly, mybe two months, maybe a month and a half. Its a goldfish. Anyways, I went on holidays last week,  and left my fish in my parents care. On Monday night, so five days ago, they bought a algae eating fish for the tank. Shortly after that, he started to become less active, and his fins were drooping, this morning, I found lil white specks all over his tail, we looked it up and realized he had ick? Now the tank he is in I believe is a 2.5L ? It's just big enough for him alone. My dad did some research and thinks that the ick was caused by my fish being stressed out from having a tank that is too small, I think it is from the other fish. What  causes ick, is it just one thing, or a combination of things....???

Answer
Good afternoon Sabrina, thank you for your question.

I was just about to sign off, but I have time to answer your question, although in less detail than my usual novellas.

You and your dad are both right, as a matter of fact. The algae eating fish, if it is a Chinese algae eater, will suck on the slime coat of your goldfish. This unsavory habit of theirs leaves red wounds, almost like welts, on your goldfish and will lead to its death or distress, for sure.
Here's a picture of a CAE for you to look at:
http://badmanstropicalfish.com/profiles/profile47.html

Even if you don't have a CAE, a pleco, another very common algae eater, will produce large amounts of waste and is not recommended for a tank even 10 times that size.
Here's a picture of a common plecostomus, or pleco:
http://www.thetropicaltank.co.uk/Fishindx/compleco.htm

Now, your dad is right, the goldfish needs a much bigger tank. These fish live for a decade (or even two) and will get larger than your fist! Besides actual swimming room, a filter and proper aeration, from an air pump and airstone, need to be employed to keep your goldfish happy and healthy. Goldfish themselves produce large quantities of waste. The solution to pollution is dilution, so a tank of about 75 L would be ideal for your goldfish, with a minimum of ~38 L.

Peruse the two sites below for information on goldfish care:
http://www.kokosgoldfish.com
http://www.goldfishparadise.com

Also read here about how to treat ich in goldfish:
http://thegab.org/Articles/IchSaltTreatment.html

Ich is a parasite, actually. These protozoans are always present in the water, it just takes stress (such as external injury) poor water quality or an accident, such as forgetting to add dechlorinator to remove sanitizer from the water, to tip the balance and have your fish break out in white spots. You can read the Wikipedia article on ich here:
http://en.wikipedia.org/wiki/Ichthyophthirius

If you need any more help I will be back on in a few hours, but I hope I have given you a lead here. Do watch out for that algae eater! I would trade him back in to the store, I am sure your parents will understand. They certainly meant well. Take care and have a nice weekend!

Nicole