I have recently bought a RO unit and experience a very fast rise in the PH of my feed water. the water straight out of the Ro unit has a ppm of 0 and a ph around 5.2. I pre-soak my rock wool cubes and slabs in the RO water that is PH'ed to 5.4. I am growing in trays with rock wool slabs and a 20 gallon reservoir that has an air stone running in it at all times. there are 3 trays with 2 plants per tray under a 1000k HPS. I have a 500 gph pump on a timer that feeds the rock wool slabs once a day for 15 minutes. here is my problem... I am using "the recipe" using GH micro and bloom. I add 6 ml micro and 9 ml bloom to each gallon of RO water. I PH correct this mix to 5.8 and add nothing else to it. when i go to check the ph in my reservoir the next day, it has a PH of around 6.6. what is causing my ph to rise so quickly and what can i do to remedy this?
and r you adjusting ur ph twice a day? first off I wouldn't say its the rockwool right off the bat. ur ro water r you allowing it to sit out before you add nutes. ro water's ph will not be stable until a couple hours after it comes out of ro. plus if ur ph rises it means ur plants r taking the food up fast. if it drops you have too much nutes and the plants start to lockout.
Tihspeed, what can i do to remedy the rock wool causing ph swings, other than using a different substrate? I do not think this is all of the problem but i am certain it is a part of it. thesage3, I am normally adjusting my ph once a day, although i have done it twice a day a couple times in the past 2 weeks. My Ro water is kept in a covered, aerated 50 gallon holding tank, it sits out for at least a day. heres what gets me, the ph will rise even when the solution just sits in the reservoir, not coming into contact with the plants or rockwool.
then I would say its either you have a lot of evaporation or a nutrient has percipated in the rez. are you adding micro first and letting fully get mixed before adding bloom? and for the rockwool you should precharge ur wool with ph water also try not running the aerator some times the extra o2 causes nutru=ients to drop out
I dont think there is much evaporation in the res as it is completely covered. I do add micro first and mix it well. then i add the bloom. the water that comes out of the RO is about 5.2. I add 1 drop of ph up to 5 gallons of RO and this brings the PH to 5.4. I then soak my rock wool in this for anywhere between a few hours to a couple days. should i be using anything else to soak the rock wool in?
RW is notorious for unstable ph, the less you use of it the better. Sage clearly spelled out all the other possibilities. Another thing that could be happening, now that your using good water the plant is drinking more causing a ph flux. Either remove the rockwool, up the nutrient strength or live with the ph swings Keep us posted No pics??
I think I remember him saying he gets the swing before the solution hits the plants which is why I asked about his mixing and aerator
I must have missed the bit about the aerator... thats a good point... don't try to take readings in massively moving bubbles... it throws off the PH pen some times as well as fluro lighting...