Hi Elon,
Quite a few reasons why this might happen.
Firstly it's better to water every day in the mornings, you say 'all the way through' so I'm assuming you mean until the water can be seen running out of the bottom of the baskets. This is definitely too much water in one go, and probably the reason why one looks as if it's dying. The best way to treat it would be to trim it back, and hopefully it will produce new growth again.

Try to keep them moist, but not soaking wet, this is inclined to rot the roots and then consequently the leaves will go 'sloppy' turn yellow and fall off.

It probably has only affected one so far and not the other because some varieties are stronger than others.

Make sure that they do not have full sun on them during the hot pm hours. - Kath:)