I've been germinating succulent & cacti from seeds for the first time. Being excited I've probably planted over 50 types of seeds within the span of 2 weeks . I've used 3 different mixes to see which works best for my area (Sydney, it is Winter at the moment but everything is indoors and room temperature is about 20 °C - 25 °C throughout the day). I've got an issue with some green substance growing and I'd love some help to remove it or what I can do. Below I'll put some details on where and which mixes grow the green substance.

1. Perlite 20% + Cactus Mix 20% + Sand 60% - Planted 100 succulent & cacti mix seeds using this method.

I've mixed all of the above together and used the zip lock bag method. I cut large zip lock bags in half and fit them around the pots and sit the pots in a tray full of water. With this method I found that majority of the zip lock bags have started showing signs of green in areas and also all the Perlite that are on the surface have turned green. Out of 100 mixed succulent & cacti seeds only 2 have germinated but shortly died from infection. Other seeds I'm assuming haven't germinated yet or have already died, is there a way to save the rest?

2. Cotton Pad + Perlite + Cactus Mix + Sand - Planted 8 different types of seeds (10 - 20 seeds per type) using this method.

For the second method I have placed a cotton pad on the base of the plastic pot then placed about 1cm - 2cm layer of Perlite and Cactus Mix 40% + Sand 60% mixed together on top of the Perlite. I think only 1 or 2 of the seeds have germinated after almost 2 weeks. I've also used the zip lock bag method for these but so far only 1 out of 6 of the zip lock bags have the green substance (no green on the mix only the zip lock bag).

3. Cotton Pad + Perlite + Cactus Mix + Sand - Planted approximately 30 different types of seeds (10 - 20 seeds per type) using this method.

My third method (which I have found the best out of the three with higher and quicker germination rate) I have placed a cotton pad on the base of the plastic pots, placed about 1cm - 2cm layer of Perlite, 2cm with a ratio of 1:3 Cactus+Sand mix then about 1 cm of Sand on top. Almost 25/30 different types of succulent & cacti seeds have germinated within 5 - 10 days. The other ones that have yet to germinate I have researched and seems like they would take longer to germinate. For this method I have used both zip lock bag and glad wrap and no green substance on any of the pots so far.

Considering this is my first time germinating succulent & cacti from seeds and majority were planted using the third method (most successful) I think the success rate is quite high. However, I would like some comments and feedback on what to do when they reach 2 - 3 months old. At the moment they are 1 - 3 weeks old. I would really like to keep them alive and if the remaining pots start growing the green substance, what should I do?

I will post some photos in the next few days for everyone to see.