I can't see that one bulb dialed down causing an issue. I got my first 1000W MH ballast and light in 1982 and have used HID light exclusively ever since for plants past the seedling stage and have grown hundreds of plants since then.
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Make sure not to add the calmag with the fresh nutes as those canna nutes should have enough as it's made for coco. Too much Ca or Mg can be the cause of lockouts. I bought a big bag of Canna coco last year and plan to do a side-by-side grow sooner or later.
Are you aerating your rez when you make a batch of nutes? Unless I'm doing DWC I mix and use my nutes right away and will discard any left over after a couple days. Not wasted but poured onto one of our compost heaps or used on plants in the veggie garden in season.
pH could definitely be an issue and is a common cause of new growth problems when micronutrients are locked due to it being out of whack mostly too high. I would aim for no higher than 6.0 when you mix up which is what I'd aim for with my peat-based ProMix HP. Peat is naturally acidic but the HP comes with enough dolomitic and calcitic lime that it can be used right out of the bale and soaked with nutes without any fuss. I also use AN's pH Perfect 3-part so haven't checked pH for anything in years and doubt my pH pen even works any more. I'm using organics these days with the promix as my base and water only with RO or distilled water as our tap water comes from a dugout on the property and is pH 8+ and 400+ppm depending on season.
