this is a question for a relative, wy is my tank always getting algea all over it when i only put the lights on for a couple of hours. no matter what i do it keeps coming back. i also have lots of little pest snails and i am wondering what will get rid of these snails, i dont want to use chemicals.
plz help

Too many nutrients, not enough CO2 or too much light is what causes algae AFAIK.

If you have snails they will be controlling the algae to some degree, best to leave them I would say.

If you don't want to use chemicals, then hetting rid of algae is nearly impossible, but control of algae can be achieved fairly simply.

I'm not a fan of snails, but they do work, but sometimes controlling a population explosion of snails is harder than than the algae.
The best this I can suggest are prawns/shrimps, I have 3 in my tank and all they do all day is "graze" on algae and the tank looks all the more natural for it.

If the tank is near a window and getting lots of sunlight that will make the algae grow rapidly. If this is the case (not saying it is), then moving the tank to another room, or keeping the blinds/curtains shut would also help.

If the snails are a real problem, then putting some cucumber or lettuce in overnight is a good idea that people use. The next morning it will be covered in the snails and you can just lift it out and remove them. Do this several times and you will find the snail problem gone. But as others have said, snails are usually good at keeping algae at reasonable levels.

Without knowing the fish in the tank, suggesting what else to put in to control the algae is difficult. Shrimp can be good as well as otto's, some plecs even.

I've got a few Amano shrimp in my tank and they do a great job of keeping the gravel, plants and ornaments clean! They can't really clean the glass though so you may need some thing else in there to help with that part of the cleaning.

I added the shrimp as an experiment and I now love them. I'll be getting more very soon.

I tried cherry shrimp in my tank, they ended up as an expensive treat for my odessa barbs, curse you LFS for telling me they would be ok, they have me some otos to make up for it though, my tank is pretty much spotless since I got the otos

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