First grow! RSQ Autos: FB, PQ, NL

You can get a ph pen. They are very accurate easy to use and cost about £30. and will last for years as they can be re calibrated.

At this stage, your seedlings roots will be 2-3 times as long as the plants are tall, so giving enough water to get that deep down is about right, and you must use a bit of your imagination to "guess" how much exactly to give them, but around 150 mls or so would be a rough estimate. I always water rather generously, giving water wide and deep to encourage the roots to also grow wide and deep. Remember too, it is better to deep water every few days, rather than light water often, as this only encourages a weak and shallow root system. Once your plants are 6 inches or so high, I would be watering every few days until there is water coming out of the bottom of the pots. This way you will know that the substrate is moist all the way through and this will keep the roots happily growing downwards. Watering to run off also helps prevent nutrient salts from building up in the soil/substrate to toxic levels and burning the plant in the future. Watering just next to the stem is also pointless, you need to water from the edge of the pot to the other edge so your plants rots grow wide and provide the plant with a good "anchor". You really need for the substrate to be evenly moist all the way through after you water and without any dry patches. Hope this helps, Organoman.