Algae: Once the canopy gets bigger the tops of the pots will be covered by it so the threat of algae is reduced drastically. Flush and start again.

PH: You don't really want PH to drop below 5.5 and not over 6.5

Temps: 74f isn't to awful bad with lights, I would go a touch warmer. 60f lights off, BRRRR!!! Dont want temps to go below 65f.

400w HPS: If I remember correctly 1m is roughly 3ft. Light is way to high, you could drop that height by half. Place your hand on top of plant and see how warm it gets.

Humidity: 50% is good for now but will need to drop to about 35% towards end.

and yes they are overwatered. Other than that looks great! :jointsmile: