6 different strains, but 1 isn't doing as well as the others...huh?

A friend I'm helping has been growing only a short time, but has run into something I can't get a handle on. He has 6 strains (all feminized seeds from Attitude) with one being Green House Seeds Hawaiian Snow Feminized. He uses the same nutes and lights and timing, but this strain has stunted growth, is spindly and looks like a Manganese problem (possibly Magnesium). All leaves, young and old, have brown spots (thick with them) on the leaves and the plants just look lackluster. Hardly ANY green, just wimpy looking. Has anyone heard of this strain and if so, could it be that this strain needs different nutes or light timing? He's supplying me for free with help, so please....HELP

got any pics? might just be a week pheno. might have to pluck it. ive grown hs out a few times and never had issues but it is greenhouse

Unfortunately, no, I have no pics at this time. If I can get over to his house soon, I'll take some. And it is an indoor "provider" grow set-up. He has it set up well and spared no expense with equipment and soil etc. So no problem with short-cut growing process. Each of the 5 plants is showing the same symptoms, so it isn't just a single plant problem. I'll look further into that "pheno" aspect too though--Thanks.