Leaves tips yellow.

It’s not a deficiency. It’s the first symptom of a the EC level starting to raise, NaCl is forming up in the soil. You’re probably not using enough water when you water the plant, and not getting enough drain coming out to rinse the extra salt out. The lemon is citric acid, and just helped to get rid of a bit of the extra NaCl, but not enough apparently. It won’t be efficient as a pH Down, your tap water should be around 7 which is good enough for growing Cannabis, just let it sleep 48H to evaporate the chlorine. And finally, your soil is a buffer and should be somewhere around 6.2, you just need to look the manufacturer details on the bag, it should be written somewhere.