Tap water, it's unsure what that water will have within it. You could be deficient on Calcium or Magnesium but that usually only happens with Reverse Osmosis or some lower PPM city water (purer water).
I would try adding some CalMag+ to your water. Botanicare makes a great one I've been using for years. I personally use Reverse Osmosis water (distilled water) that has nothing in it, so I do have to supplement CalMag & Iron when growing in Coco depending on what nutrient line I'm using.
In coco you should be shooting for a more acidic PH of 5.5-5.8. On a liquid tester kit you should see a light yellow color ideally. Organic Nutrients tend to be quite acidic though to begin with so I'm curious if that + citric acid is causing a ph imbalance? Keep us updated please.
Also, if you're worried about Chlorine/Chloramine you may want to let the water sit overnight before use OR consider investing in a Reverse Osmosis water setup. I can recommend Hydro-Logic RO-150 or RO-300 for starters. The entire kit > tank > hoses should only run you a few hundred bucks and last you a lifetime. Then you'll be in entire control of your water and what is in it and have less guess work.
