In my opinion, using distilled water is causing the problem. Distilled water has nothing in it, unlike "normal" water which has dissolved minerals in it. By using the distilled water, the water will actually "suck up" soluble minerals to once again balance its composition, including sucking minerals from within your plants cells, causing a decline of nutrition in your plants. Water them with normal water and they should pick up soon enough and maybe give them a very weak dose of nutrients, around 10% of recommended rate and this may also liven them up, for as you know, neither coco coir or perlite have any naturally nutrients in them.
Hope this helps,.... Organoman.