Critical O P grow

Ok so I had a fairly routine week until I discovered a problem up top! The new growth leaves at the bud sites were showing signs of nute burn, after checking my runoff the problem was clear as my runoff was at a nasty reading of 3.0ec! After reading up on the cause/solution...(no pun intended) I flushed with a 1/4 strength solution and ran 5L through to get the run off back to 1.7. Her vertical growth has finally slowed and just in the knick of time as there is very little room left to raise the lamp. Apart from that I am having to really keep on top of the humidity, my dehumidifier is struggling to keep levels below 50, I have another that can do it but that one throws out hot air and raises the temp too high, even with the extractor on. This will need addressing soon. Thanks for reading, have a great week.