Sorry, but THREE goldfish AND an algae eater is NOT a good stocking for a 10 gallon.
Goldfish are VERY messy fish and create a lot of ammonia that can be fatal to your fish. I suspect you haven't done your researching, becasue you need to let your tank go through the cycling process for about 1 or 2 months. One goldfish needs about 20 gallons, and then 10 more gallons for every goldfish after that.
Please try to return at least 2 of your goldies and the pleco.
You probably bought a common algae eater, a pleco, that can grow up to a foot! I've seen huge ones in stores. They also do not eat much algae, as they become more aggressive and eat less as they become older.
When you do your water changes, does the replacement water have water dechlorinator in it? The chemicals in tap water can kill your fish and make the water murky.
