First grow - light green sapling with reddish stem compared to my newer sapling. What’s wrong?

it's in an inert medium and you have not fertigated... I feel like you can figure it out from here. your tap water isn't idea but it is not causing this. My tap is ~300ppm according to local quality report. I've even started using soft water, lol. The levels of chlorine or chloramine in your tap water will never cause a problem with a plant unless it's some mother-plant stuck in the same pot for years... even then if religious aobut runoff, any related problems to Cl could be avoided. The plant actually makes good use of a very small amount of chlorine. macro nutes are used in millimoles and trace elements, like Cl, are used in micromoles. You need to fertigate every single irrigation when using coco or any other soilless medium. It needs to provide a complete, well-balanced diet. 10% runoff, religiously, will prevent buildup. It's that simple. Take notes and fine-tune your formula based on symptoms and growth patterns. If systematic, should have a well-hammered out formula by your 2nd cycle... poor instructions from brand might set you back but eventually trial and error will get you there. I've tracked elemental ppm of each nutrient molecule since is started growing. At this point i understand upper and lower thresholds of most realtive to me local variables. Your climate and atmospheric co2 levels will cause different overall concentration neeeds, but the basic ratios will be similar. the goal for each nute molecule is to be readily available in proper concentration while not impeding other nutrients. Mulder's chart give a visualization of the complexity. More is not better, and coco does not change what the plant needs -- common repeated bro science nonsense. Check out cocoforcannabis.com for excellnt guides for soilless growing. By far the least amount of bullshit infused guides on any marijuana site.