1st ph for hydro is 5.8!
Some growers "like me" lower the ph to 5.4 in week 3-4 of flower and work back to 5.8 to help make bloom enhancing elements more available to the plant. It has nothing to so with seedlings or vegging...Optimum ph for Hydro is 5.8

In answer to your question.
1st you need a ph meter or pen in order to read the ph. ebay 20-100 bucks.
2nd you read the meter and determine the ph of your water or mixed up solution. (A lot of pro nutrient mixes contain a buffer that helps to stabilize the ph of solution)

Very seldom will the ph be low. It will usually read high. water is around 7.0 this is too much alkaline for Hydro roots. so you add a little bit of ph down at a time, because you don't want to overshoot your mark and have to add ph up...bad for the plants.

Anyway; It depends on the size of your rez, but you can add a 1/2tsp to a tsp at a time until you get the hang of it. After awhile you will be able to gauge the amount of ph up to use in order to get close to correct ph, then you can tweak it to 5.8. Hope this explained it for you. It is pretty basic. peace:smokin:
latewood Reviewed by latewood on . How do you Measure pH up/down solution? Hi all im a new grower just starting out and I have a 8 bucket water farm with a 8 gallon texas controller and a 17 gallon reservoir just to let ya know what im working with. I have been searching the internet plus these forums like a madman and I couldnt find what im lookin for. The usual pH range from seedlings and vegging I heard is 5.8-6.0 but the confusing part is how much ph up/down do you measure out to get it back to that range from a high alkeline or from a high acid. I tried searching Rating: 5