You could nest two tubs with drain holes in the top tub. As far as the water, something I have noticed with some strains that the hard water combined with high ec nutrients can create a condition that looks like deficiency and nute burn at the same time. With mmj you won't need ca/mg unless your leaves taco and the edges curl up like cupped or embossed edges. The reason so many peeps use it is because they are using RO water. Personally I think that is going to far, that is a completely different rant. It is cheaper, easier, and less wasteful to filter down to what you need. A cheese cloth (washed once a week), and a britta filter will remove chloramine and as much as 25% tds. It adds a step but the results are well worth it irrespective of the media you use.
FYI, I can see much improvement in your work. The next step is as stated by others, get the light off the roots. That stunts root growth and uptake, the roots don't like any light on them. They start to convert to stalk, they can even turn green trying to photosynthesize. These problems don't even account for the algae......
Eventually you will have eliminated all the environment variable issues but in the end it can be more work than soil/less. It is arguable as to the value of what you gain from hydro anyway. Commercial goals are the recipient of all that hydro has to offer, the quality aspects will always lean toward soil/less and organics. Why coco? Plain peet and pearlite is cheaper and better imho. Still soil-less, a shake of some dolomite lime and you have the best of both worlds (hydro/soil). Coco is so trendy the price has gone up, at the right time and place you can get 3 cu.ft. of peet moss/sphagnum moss for $3-4 and a cu.ft of pearlite for $5. That's a light mix, water every other day. Alternate your tea and nute soln. Add a plain water to the cycle for a week or two after a transplant.
Oh ya, have you leached your mom with some clean water? If not, do so and if you have some flushing soln use it then give her a little lime and a feeding.