I was recently told that it is possible to use miracle gro to dose a planted tank, is this correct? I was told that it would not harm any of the fish and that it would be an easy alternative to ordering fertilizers to dose with
Ph out of the tap is 8.6, so no worries there, I'll go ahead and check the box I have lying around and see if it's any good!
i meant to say urea or ammonium based fert become problem if Ph is higher than 7. yours is already high enough to convert ammonium or urea into ammonia within seconds after adding to the water. i wouldn't suggest adding this fert in that parameter.
As people have already mentioned, I would highly recommend you not using any (terrestrial) fertilizer that uses ammonical nitrogen (urea) as its nitrogen source, since it will become ammonia in your aquarium (at a pH of 8.6, there will essentially be no ammonium anion formation).
There have been people that have successfully dosed with urea, but I do not think they ever dosed when there was livestock in the aquarium.