I would recommend changing the media.
Bad leaves can be an indicator that something is not right in the root zone.
Cut away any roots that don't feel firm (brown is usually a good indicator but not a definite sign the root is bad)
Otherwise too strong light seems to make spotting worse but it is probably due to the roots not being able to keep up with the light provided so I would inspect the roots first, if they are in bad shape then provide less light till the roots recover.
Be very sparing with nutes, even tap water can cause salt build up if it has too high ppm.
Feed when you feel like leaves are too light of a colour or when in active growth but very sparingly. Too little feed is always better than too much.
Ps: adding mag and calc is good if you main nutrient lacks it but getting the ratio right is tricky, I would switch main nute otherwise you could end up feeding too much mag and calc and cause even more issues.
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MJG 
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