Ive a 140l tank with my standard tap water ph of 7,is there a calculation i can do to determin how much ph down to use,and is there any tips or triks for getting this perfect,i hate this randomly throwing in a few mill here an there,so any advise would be great!
Sorry to say... but there is no "set" formula to adjust your ph. I have been growing hydro for about 4 years and it took me about 3 to 5 crops to get a proper feel. Reason being is that your nutes are constantly on the move. The level of nutes changes daily... so you start with 140l and the next day it might be 132l then the next 124l, depending on how many plants you have and how much they drink.
Also, your water is completely different from my water, which is different from Shmo's water... etc. My nutes require me to add approx 1 tsp (5ml) of ph down about every 2nd or 3rd day.. where as my bro's (in a different town) requires him to add about 2ml of ph up every day.
You have to keep a diary or log book of everything you do to your nutes. This way you teach your brain over the course of learning. Learning to grow hydro
"well" actually has a
steep learning curve. Anybody can grow something in hydro, but growing it
"WELL" takes a bit of learning by doing. But once you have learned it... life is good.
If you want accuracy, get a decent test meter like a Hanna HI 98129 or HI 98130. Well worth the investment if you are serious about success. I use the HI 98129 and it works very well. Also make sure you get the proper maintenance solutions that go with it (cleaning solution, storage solution, calibration solutions).
If you just wanna grow "sort of" hydro... then disregard the above paragraph.
Hope this helps. Cheers!