1st off, which type of algae is it? If your unsure then this link may help
http
/www.theplantedtank.co.uk/algae.htm
I have a planted tank and i have had just about every form going! I get on top of one type and another takes hold! I have it all clear now but you do have to persist to get rid of it.
2nd. What is your set up in regards to lighting, co2, planted or not, stocking, how long has the tank been set up etc.
Un stable co2 is more likely to cause algae than low co2. Co2 issues are usually associated with high light tanks. Sun light can cause algae too, but if moving the tank is not an option then your LFS will sell a reflective backing you can put on the back of you tank which the sunlight cant penetrate.
If your stocking is very low and you have very low nitrates that could also be a cause. Poor water circulation and dirty substrate are other contributing factors.
I wouldnt worry about the snails at the mo. Getting you water chemistry right is the most important.
Good algae eater are snails, ottos, amano shrimp. hungry fish too