listen to pokey. Your plants are underwater, the color looks fine but pretty soon your going to need more food. Digging around with your finger isnt a problem unless your getting crazy with it. But lifting your pots is equally as easy i f your worried.Your plants are not under fed or in need of hydro store snake juice. Under watering can cause a slew of issues, best to start with the glaringly obvious problems. First pick up your pots and remember how heavy they are. You can even weigh them if you want. To find out how much water you will need you can water slowly until run off, your soil looks rather dry and if i can tell that from the photo your media is hydrophobic on top no question. Your going to want to water cup by cup allowing it to absorb fully before adding more, the soil drys back and leaves gaps in between the pot, dumping two gal of water on it will just run off the sides. Do this until you have a small amount of run off, and only do this this one time, you do not want run off. After your plants are hydrated watch them, over the next few hours they will start to perk up, or pray, rising their top leaves up. Watch for this change carefully, and then in the days to come watch how the leaves start to drop from praying and water based upon what your plants are telling you. No calculation can tell you how much water a plant needs, and those needs will constantly change, you must learn to read your plants. Now with your hydrated vessel pick it up and feel the difference.