Okay Em, thanks. I think the Miracle grow...Mg as in magnesium. The miracle grow is probably the cause. Not to worry, easy on the water, mine use about 1/4 cup per day at that size...tops.

Next pot size up should be about a 1 -1.5 gal nursery size. See if ya can find some potting mix without time release food. You must go very, very easy on watering as each time you water you release nutes in these mixes. Do not just go to huge pot, water settles to the bottom and gets stagnant.

But regardless I think these have grown beyond the age I mean when I am talking just sprouting out of the ground and the red. Note the duskiness below the cotyledons on these two young girls. Note how the red on the petioles only is mostly on the top half and just dots.

Of course this could all be just lighting differences.

Yes I have given up on filtering. But what is in your water?

Yes as the root system builds the needs of the pot of soil will increase and of course without a good root system less water will be used.