A few suggestions. Are you up-potting on a schedule? Up potting is important. The pH buffering capacity of soil will depleted over time, volume dependent. Up potting replenished the nutrients and buffer capacity for the next stage of growth. You should be starting in 8 - 16 oz containers, after 2 weeks up-pot to 1 gallon for the duration of veg and then up-pot again just before or just after flipping to flower to either 3 or 5 gallon pots. 3 gallons is usually sufficient for the average hobby grower. Consider buying a fortified soil. You can reduce your nute input by 75% reducing the likelihood of salt build up and you start with a soil that is properly buffered. This will help with pH over the longer term. I highly recommend FoxFarm Ocean Forest. I veg for 6 - 8 weeks. They get only 2.5 ml of grow formula 2x during the last 2 weeks of veg. In flower they get 4 weeks of increasing strength bloom formula starting at 5ml / gallon and topping out at 10ml / gallon weeks 3 - 6. Not much at all. This is because the soil is fortified with a range of nutrients. I used to face periodic pH issues. I have been golden since I switched. Note nute strength is strain dependent so you will need to figure this out as you go. Are you watering when you think they need water or when they are actually ready for water? They benefit from getting pretty dried out. Next time you water lift the pot. Note it's weight. Lift the pot before you water to gauge the weight when it's dry. Over time you will gain a feel for when it needs water based on the weight of the pot. I water 1x every 3 - 5 days depending on their stage of growth. More in flower, less in veg. Again, this is strain and environment dependent. Try to stretch your water schedule a bit. If you are using RO water then be sure to add some unsulfered molasses to your mix, especially in flower but take care as it acts like a multiplier for other nutes. Keep reading and good luck!