Experiment : PH fluctuation - Need HELP

Hi guys,
i got a problem i need to solve before starting my new grow.

This is what i do :
I take a glass empty bottle and i fill it using tap water.
I check ph and it's 7.0
Then i correct ph using phdown until i get 6.2
I check ph AFTER 12 hours and i get 6.9.
My question is : Why ?
My second question is : Assuming the problem is my tap water if i change it to RO water i should solve the problem ??

Thanks

Add dolomite lime to your soil mix this should correct your problem. I dont think the problem is your water if you correct the ph by using ph down. Sounds like a salt buildup flush with ph water and if you can add lime that should fix your ph problems 1-2 tbl spoons per gallon

tmbt said:

Hi guys,
i got a problem i need to solve before starting my new grow.

This is what i do :
I take a glass empty bottle and i fill it using tap water.
I check ph and it's 7.0
Then i correct ph using phdown until i get 6.2
I check ph AFTER 12 hours and i get 6.9.
My question is : Why ?

Click to expand...

It's alkalinity, a.k.a. buffering capacity. This is called pH bounce.

My second question is : Assuming the problem is my tap water if i change it to RO water i should solve the problem ??

Thanks

Click to expand...

Yes, or, you can filter through peat moss, or use one of the aquarium industry products to get the water buffered down. However, if you're growing in soil, I wouldn't worry about a pH of 6.9 very much, the soil tends to self-correct/adjust anyway.

Do not use dolomite to try to bring the pH down, it will do the opposite and will add to its alkalinity (buffering capacity). Mineral content is the usual reason/cause of well-buffered water. In fact, we use crushed dolomite for saltwater or high pH-requiring animals in aquariums in order to keep the pH high and the water well-buffered (pH shifts as low as .1 can kill some fish very, very quickly).