howdy fella. just popped in to look at your plants. have a few comments to start us off.
ok first off. over watering often has little to do with too much water, but rather a lack of oxygen. as the problem continues the little hairs on the roots shrivel up and die making it very difficult for the plant to take in water.
the best thing to do is dry your soil.
the second best thing is to infuse it with oxygen.
those mixing buckets are EVIL for waterlogging plants, they dont breath in any shape of form.
drill in lots of holes, especially at the bottom and raise it up on a couple of bricks or something for air to get underneath.
at this point your plant looks too far gone to wait for dry soil. i reccomend purchasing some h2o2 (hygrogen peroxide).
if you buy the 3% type. mix this 1 part to 4 parts water. this concentration has done no harm to 3 strains for me so far.
this will replace the current water in the soil and allow the root hairs to breath.
the added ventilation should help the soil to dry out then.
growing multiple plants in a single pot is not reccomended. as you can now see what one suffers all can suffer. plus roots can choke each other and kill all the plants. communally grown plants should have a good amount of space between.
that is a huge volume of soil to try and dry out by the way. i believe your best option is to transplant into seperate pots.
whatever you decide, your going to need to pay close attention to adding oxygen to your water if you cant get it to dry out fast enough.
if you use that tub again in the future, i reccomend half filling it with pure perlite before adding soil. that combined with drainage holes should eliminate the problem in future =)