if youre new at growing, the last thing you want to do is mix your own soil. Your soil is the most important thing to your plant, especially container growing.and you want to use the best you can buy, especially if you're not experienced. I use promix brk with biofungicide and mycorrhizae for all my plants in the spring. I switch over to baccto for summer growing and fall growing when media isn't so critical.
if you're having algae in your media, then you're overwatering or using bad soil to start with that has been wet before you planted it. keep your soil dry after purchase, and inside, not outside, at least if you have to keep it outdoors, cover it tightly with tarps and keep it dry. if deer ticks are climbing into your plants, then you need to tighten up your greenhouse. We put screening on the sides of our greenhouses this year. we are installing screen doors, like in a house, on all of our greenhouses instead of propping our 48" doors open to keep out bugs. Also customers understand how to close that kind of a door and open it...so they will stay closed.
Fertilizer, you want to use a 20-10-20 at 200 ppm every second or third watering minimum. That works for most plants. and adjust your water ph so that it's effective, especially if growing petunias. We use two different fertilizer injectors, injecting acid to adjust the ph, then fertilizer, and in one greenhouse this year, we have three, because we have more acid for the petunias fertilizer to keep their leaves green.
we do annuals/veggies for spring, perennials for summer market, and herbs all summer, mums for fall and houseplants for winter, and of course being Northern Tropics, we have tropical available always....lol...pm me in fall if you want to talk more, I don't know why I have time to talk this much this time of the year anyway. IN two weeks we don't have time to even eat.