A month for that type of growth on from bare root plugs seems normal to me. Figuring a couple of weeks to wake them up, then another couple to get some descent leaves on them. But I'm not sure why only 3 out of 10 grew. You can lower the water level but be sure to watch the plants (so they don't dry out/wilt). If only a quarter inch of the basket is submerged, there should be plenty above the water line, and if the water is aerated sufficiently with an air
pump and stones, there should be sufficient oxygen in the water also. That's the idea behind a "Water Culture" system in the first place (Deep Water Culture "DWC", is the same thing).
But strawberry's are susceptible to a lot of problems. I cant tell from the pictures, but I'm wondering if the crown is too wet. The crown is the part where all the stems of the leaves originate from. Strawberry's don't like for the crown to be consistently wet, and leads to disease and fungus problems. Judging by the pattern of the browning of the leaves I think this might be a problem, and in a
hydroponic system diseases can spread from plant to plant very easily through the
nutrient solution itself. What do the roots look like? Brown, slimy and/or mushy is a real bad sign.
It looks like you are using rock as the
growing medium, rock shouldn't wick up that much moisture to be much problem. However the rock looks wet at the top, witch is why I'm wondering if the crown is too wet. I used coco chips witch hold moisture well, and the water level was about half way up the baskets on my strawberry's (I attached some picture of them).
It looks like there is a lot of dead organic material around the crown, that can hold moisture and add to a problem. You can trim the dead stuff off, and raise the crown up a bit. I think that would help more than lowering the water level. Also air circulation around the base of strawberry plants helps against fungus problems. As for the 400 watt MH, what's the air temperature at the plants foliage (what there is of it)? And I'm not familiar with the directions for those
nutrients. But for plants that small I would probably just use them about 1/2 strength, no more than 2/3 strength anyway.
But realistically at this point with only 3 out of 10 plants beginning to come to life, and even those leaves are turning brown. I would probably just cut my losses and start over. Completely clean and sanitize the system, including the baskets, growing medium, air stones etc.. Then go down to the local nursery and buy some already started strawberry plants. Gently wash off the soil from the roots, and transplant into the hydro system. No sense in wasting a lot of time, nutrients, and even electricity running the
lights at this point (the way I see it anyway).
Sure there's a possibility of introducing soil born diseases into the hydroponic system that way, but that's actually no different than using bare root plugs. Bare root plugs were started in soil also, then they just washed it off before shipping to you. The difference here is you don't need to wait a month for store bought plants to come to life and grow some leaves.