Your plants look like they be getting a high tds. Algae feeds on excess nitrogen and seeing how your leaves are yellowing and the tips are burning I would say that it may be a cause. If you reuse cloning cups you will get algae but its from being constantly moist. I would not worry to much about it messing up your ph. The roots need to breath sure and I dont know if benefical microorganisms for the rhizoshpere may help break it down around the roots or not. Mycorrgizae may help as well to expand the root function. Be carefull not to over water. Baby organic soy formula with its calcium content my help aswell.
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