I have my 2 plants in 5 gallon pots with Pro-Mix Potting soil. The bag of Prom-Mix mentions that there is fertilizer already in the soil good for 9 months. My plants appear to be growing well, and at week 4 I decided to feed them 5ml of Reefertilizer Grow per 4 litres of tap water. The ph of the nutes+water is 7, and the runoff is 5.5. Is this runoff too acidic? Should I UP the ph of my nute solution, or stop adding any additional nutes, than what's already in the Pro-Mix? Thanks!