Green water in an aquarium is nearly always caused by an free floating algae in the tank. The two things that can make them reproduce quickly enough to turn the water green are too much light and too much nutrients in the water. The snail explosion may contribute to the problem. While it is true that they will eat the food in the tank that the fish miss they also produce waste after doing so. The uneaten food, fish and snail poop in the tank will all add the nutrients that the algae needs to grow. Also, I am assuming that the algae has nothing to compete with. You rarely see green water in heavily planted tanks because the plants will use the nutrients before the algae does. The easiest way to get rid of the green water is with massive water changes and be sure to vacuum the gravel well.
Also, blacking out the tank by keeping the lights off and either placing a blanket over the tank or taping dark paper over the side panels will kill the algae (and any plants you may have in there). While the tank is darkened you can put zuchini slices or spinach on the gravel. Many of the snails will climb on for a meal. Your can then pull the veggies out and get rid of snails. Going forward, make sure you are not over feeding your fish and don\’t allow more than 10-12 hours a day of light. Adding live plants to the tank will also help. Java ferns and java moss grow well with standard, low wattage aquarium lights. On the plus side, the green water in your tank is very nutritious for young fish. If you are growing out any fry it can be used as food.
I think one of the problems with algae is that everyone makes it out to be a problem It s not it s normal.
There certain things that can make it grow in excess, but everybody has to deal with it and it s the product of a healthy tank. You vacuum the tank every 2 weeks, that s a good thing. You should be doing a partial (20-30%) water change at the same time right? Don t be afraid to clean the tank once per week water can t be too clean and for the 20 minutes it takes, why not? Make sure you are not overfeeding this is one of the most popular reasons for tank problems. No food should go uneaten, and fish don t need to be stuffed to the gills every feeding a lot more food goes to waste like this waste in the tank, that is. Also, a lot of people buy algae eaters thinking it will cure their problem algae eaters are one of the messiest fish out there they add a lot of bioload to the tank and usually stop doing much for algae after a while, if they ever did.
The simplest solution is sometimes the last one people think of. Turn the lights off. Without light, algae can t thrive. So instead of using the aquarium lights, just use indirect room light instead it s plenty for the fish to see by. Feel free to turn the aquarium light on any time you are actually around to view the tank. The only tank light I keep on all day when I m not actually around is my planted tank and algae for me is something that grows so slow it only needs a light scrape every few weeks. I don t scrape it off the decoration on purpose because the tank looks nicer and more natural this way everything really belongs.
If you do have plants and cutting down light isn t an option, then you should add more plants, so they can use the nutrients in the water before the algae can. Faster plants use more nutrients then slower. As for emptying the tank to clean it it is hard work, and stressful and dangerous to the fish a properly maintained tank should go years without this. Just scrape it off the glass and decorations with the tank intact. Heck, if only people would recognise algae as the most natural element in a tank that actually exists in the fishes natural habitat, they might actually learn to like it and appreciate how natural it looks compared to a perfectly sterile and sparkly new setup.