How to change the ph from 7.5 to 6.5?

Like he said get ph up and down. Use small increments at a time ex: 5ml at a time or less depending how much you have to adjust.

Earth Juice carries both items I mentioned as part of their line of pH buffering products.


This is simply not true! Phosphoric acid if used in a well buffered solution WILL NOT kill your microbes! It becomes phosphate as the H ions are stripped off and balanced with the counter OH ions in the solution. That’s how it works as a pH down.

Contents of GH PH down:

Guess what the soil was not wet enough. I am off to the garden stir for a soil test kit. I was using a mechanical tester. Good for wetness and light not ph. Thanks to all for the good advice.

Watch Your Temperatures

Phosphorus uptake is temperature-dependent. If your nutrient solution is too cold, plants won’t take up adequate amounts of phosphorus. Plant growth will stall, and the stems and undersides of the leaves may even start to turn purple. When using phosphorus fertilizers, carefully follow dosing directions and try to make sure the nutrient solution stays above 58°F. For best results, maintain the nutrient temperature between 68 and 75°F.

Don’t Overdo It

It is possible for plants to develop phosphorus toxicities. If excess phosphorus starts to build up in the reservoir, plants may take up too much all at once. There are no direct symptoms of phosphorus toxicity—it shows up first as a zinc deficiency, then as an iron or magnesium deficiency. One reason phosphorus levels become too high is the addition of phosphoric acid to the solution. Many hydroponic growers use phosphoric acid to lower the pH of their nutrient solution, but since phosphoric acid is actually a phosphorus fertilizer, it can quickly build up to toxic levels if too much is used. Moderation is the key.

Phosphorus additives are beneficial when they are used in the correct amounts at the correct times. Learn to spoon-feed your crops to give them exactly what they need when they need it. A little extra phosphorus can energize the rooting process and stimulate the flowering process, but too much at the wrong time can have adverse effects. Manage your phosphorus fertilizers wisely and your plants will reward you with heavy yields of vibrant flowers and tasty fruits.

1 Like

I use citric acid when I’m just using ph water. It takes about 1/4 tsp for 3/12 - 4 gal. None needed when I’m feeding.

General Hydroponics Ph up and Down is not recommended when you want to maintain a healthy living soil. Many many suppliers of living soils go out of their way stating not to use chemical versions of anything and the Critic acid is cheaper. When it comes to Hydro growing I don’t do that so I’m not versed in that at all.

Alaska ph down works well. I picked some up on end of season clearance at Walmart for cheap.

I prefer to use an unfiltered organic apple cider vinegar with the mother. Works great. I tried using Alaska ph down but feel ACV works better.


Hoping I’m not hijacking the thread here @TommyBahama… But I have a quick one.

Slowly ingesting all this info on pH and trying a real world scenario today…

My water is pH 7.3 from the tap. I tested my runoff and it’s about the same, I think, though I did see some aberrations of up to 7.7. anyway, i attempted to ph down with white vinegar and that number is just not budging from about 7.1

What could be keeping a 5 gal, newly mixed with ffof, castings, kelp meal and perlite from dropping into the 6’s? I’m on the 5th flush, now with the water phd to 4 just for the hell of it!

I also use apple cider vinegar. I don’t know about the white vinegar. Luckily my current well water is so close it does not take much to adjust it.

Water has no buffering capacity to change the pH of the soil. You need phosphate buffer at a high enough concentration and pH 6.5 to absorb the OH ions being given off by the soil likely from lime that is slowly dissolving.

Do you have a source of this information? From a biochemical perspective this does not make sense. Phosphates are everywhere. They may have been referring to concentrated acids/bases killing microbes…this is true, but not properly buffered phosphates.

1 Like

Sorry, was that reply directed at me @WickedAle?
Does it help to know that my ppms went from 3000+ ( ffof, holy smokes!) to just a tenth of that now around 300? If ppms reached a theoretical 0, would the pH start to move, assuming it’s lime dissolving?

You have probably flushed all of the goodness out of the soil if you have dropped your PPM so low. Soil will give off some PPM higher than 0 even if most of the nutes are gone, but it also requires time to dissolve. Also what is the PPM of your water?

As for pH 7.1 it is a bit high, but it is not so far out of the range you will get complete lockout. Lower pH (below 6) is more of a concern.

Ppm of tap ( not RO or otherwise filtered/conditioned) from the hose is 15. Crazy but confirmed on two separate meters. Watershed is pristine apparently.

I am sure I’ve leached all nutes out but I’m trying to get the pH down and I don’t understand why it’s not responding. Should I spring for some pH down, will that have a better effect? Or do I just need to continue flushing with (vinegar’d tap water) 6.5 until the number drops. Seems crazy that I’d need to do this with ffof to get the correct runoff range.

As I said. You won’t be able to change it with water no matter what PH. You need a nute solution with a high enough phosphate concentration to buffer the counter OH ions being released (likely slowly) by the soil. Not by simply flushing. Flushing washes away all of the “goodness’ the plant wants to grow on.

Then I think i must be totally missing the point of people flushing to adjust for soil pH issues. Or is your point that my problem is unique? Sorry, I am definitely not well versed in this stuff.

Flushing is used to reduce salt buildup in the soil/media (nute burn). Feeding the appropriate pH nute solutions bring the pH balance to the soil (and nutrition depleted from soil to plants.)

Understood. So, perhaps it’s not that common, but I have been reading about people adjusting soil pH with water that has been brought up or down accordingly one way or another. Granted, it’s not necessarily always to the point of “flushing” but this is sort if an experiment and a way for me to grasp the concepts of pH in a growing medium. The plant has been a runt for weeks and considered a lost cause, so I figured what the hell. Now id like to figure out how to most efficiently bring my medium ( in all my pots, not just this tester) into optimal ph range. I’m not feeding anything, given the hot nature of this soil. So how might I go about bringing that runoff down to the correct ph levels? If it’s a nute solution, is there something you’d recommend, considering I’m 5+ weeks in veg?