You don't have to water a plant that small everyday even if you are in coco. When the plants get bigger and have a decent root system then you start watering everyday.
The perlite is turning green from algae because the coco is just staying wet and the plants are too small to uptake the moisture in the coco. You're basically just pouring more nutrient solution into already saturated coco. When the plants get bigger they'll suck the coco dry. Coco or soil if the perlite on the top is growing algae then you're keeping it too wet.