Algae is a very broad term for a wide range of organisms. Each one has its own causes, and treatments. One so-called "algae" is actually cyanobacteria, but is commonly referred to as Blue-Green Algae (BGA). All algae benefits from excess light. Ammonia can lead to some algae. Fluctuating nutrients can lead to others, depending on what nutrient is fluctuating, which algae will show up. I mentioned earlier that I had a bit of BBA (Black Beard Algae) from fluctuating CO2 and low flow. Increasing flow and decreasing water change frequency stabilized the CO2, and the BBA disappeared.
New tanks often suffer, because of the connection between light and ammonia. New tanks (except for those properly planted for a silent cycle, not recommended for beginners, or that went through a fishless cycle) often have ammonia issues as well. The light plus the ammonia leads to algae. There are very different types of algae, but as waterdrop points out, too much light is always culprit number one to finger in these cases.
He was dead on accurate. You have a lot of light. The wattage isn't so much the issue. The duration most definitely is a problem. Fish don't need light, so the light is only there for you to view the fish and for the plants to survive. But, too much light is also bad. You need to cut your hours back. I would say to cut is all the way back to 8 hours. Choose the 8 hours that you are going to see the tank the most, so that you can enjoy it. There's no sense having the lights on the tank while you are at work all day. The fish don't care and you can enjoy the tank with the lights on in the evening. Personally, my lights are on from about 3:00pm to 10:00pm.
As far as your amount of wattage for the tank - there are a lot of things that go into this. First, the wattage isn't actually as important as the lumens, and the amount of lumens put out isn't as important as the amount of lumens that actually reaches your plants. Ultimately though, an underwater lumen sensor is rather expensive and isn't a necessity on an on-going basis so it is a bit of luxury item for a hobbyist. Professionals who set-up planted tanks for high paying clients would be stupid not to have one, but for the individual, just being more vigilant about the health of your plants is the way to go. So, we fall back on the Watts/gallon ratio. There are different levels of light and they match up with different plants. There are plants that require high light (meaning high W/g ratio, over 2W/g) all the way down to low light (less than 1W/g). You need to have a balance between the light output and the plants you are growing. If you have high light plants under low light, they will generally just break down and die (melt, as it is called). Your light is moderately high, and with 12 hours of duration, I can see why your plants have grown so much. You need to ID your plants. You need to know exactly what plants you are dealing with so that you know what type of light and care they really need. Take some pictures and post them either here or in the planted section.
(For myself, my tank has just 28 Watts, it is a tall tank (24 inches), but 56 gallons. I have less than 0.5W/g. That means I can only have very low level light plants. They grow but fairly slowly, the exception to that is my anacharis. It still grows long, but not very full. The plants have become much narrower than when I bought them... also known as leggy in the plant world. If I were growing tomatoes, I'd worry about it. But, since the water column holds them up, they are fine that way.) The rest of my plants are very slow growing, low light plants. Java fern, Amazon Sword, Anubias. These plants will grow in any condition, but are just fine under low light with a very slow growth rate.
Here is a link to the very best source of information on algae I've found.
Lfs didn't have apple snails, got some more amanos ( love these shrimp). Pwc 20%. water is good at the of the day- 0/0/20. Will leave lights on for 6 hours for the week.
