Ok im trying to get hold of a digital ph pen but looks like i may have to get it online.. in the meantime i grabbed another ph tester that has the metal rod and the dial.
The device i got is meant to be for soil however but i did test the ph of the tap water. After a minute or so (the time it says to leave ot in soil) the ph was showin 6.2 however if left longer it would eventually go down to 5.2 at which point it would stop. im guessing this is the true ph of the tap water?
I then checked the ph of the soil and the ph of the water in the tank (with nutes) and both times the dial remained on ph 7.

In the last few days ive done what you said and watered by hand untill i see a little run off and then let it dry out. ive found myself waterin twice a day.
The plants seem to still be growing fine and the new leaves look healthy but the bottom bigger leaves on the main 'bad' plant look in a bad way.

Ill post some recent pics....

Really appreciate the help