Science question re: pH

[H20gro]

So if i use hard tap water w a ppm of 450, it takes a substantial amount of ph down to get it in range.

If i use RO water w a 7+ starting ph, it takes… drops… of ph down to get in range.

Why?

Thanks in advance for your help.

 

[Peat Phreak]

Because RO water has no bicarbonate to neutralize acid. You don't need to pH RO water unless you are growing hydroponically. If so, you can add some CaCO3 to buffer the acid.

 

[H20gro]

Because RO water has no bicarbonate to neutralize acid. You don't need to pH RO water unless you are growing hydroponically. If so, you can add some CaCO3 to buffer the acid.

I am growing hydroponically. Are you suggesting calcium carbonate to raise ph as needed or????

 

[Peat Phreak]

I don't grow hydro and could be wrong about what to do.

Creating a stable pH for the roots is not easy to do without a having a base. Like you said, just a few drops of acid can be too much. That is because there is no base.

I think you want to have about 50ppm bicarbonate for pH stability. Instead of CaCO3, you could try something like 15-20% of your tap water plus RO. Then add acid.

 

[Peat Phreak]

100-200 ppm of potassium carbonate is what this very reliable hydro source recommends for RO water.

https://scienceinhydroponics.com/2020/05/understanding-the-carbonic-acid-bicarbonate-buffer-in-hydroponics.html

 

[SamSmith]

More good information from PP. If you use straight RO through a good unit resulting in 0 TDS you can be in for a wild ride in DWC PH wise without some type of buffering in the mix.

 

[H20gro]

100-200 ppm of potassium carbonate is what this very reliable hydro source recommends for RO water.

https://scienceinhydroponics.com/2020/05/understanding-the-carbonic-acid-bicarbonate-buffer-in-hydroponics.html

Interesting, if not complicated, read. Thank you very much

 

[H20gro]

More good information from PP. If you use straight RO through a good unit resulting in 0 TDS you can be in for a wild ride in DWC PH wise without some type of buffering in the mix.

So mix the ro water w about 20% tap water…. ? Thats kinda my plan at this point…

 

[SamSmith]

So mix the ro water w about 20% tap water…. ? Thats kinda my plan at this point…

That sounds like a plan. I am still interested in what exactly makes up your tap water ppm. Can you pull a report from your local water treatment plant?

 

[H20gro]

That sounds like a plan. I am still interested in what exactly makes up your tap water ppm. Can you pull a report from your local water treatment plant?

I have tried to get that report online as ive seen other cities reports. Not easy to find or read what is available. I suspect it is high in iron bc toilets get a brown residue/deposit…. But not sure. If i can get the report i will try to post it

 

[H20gro]

So i just mixed an 80/20 ro/tap. The tap water brought ppm to 90. Mixed a weak nute solution and got ppm to 500. Ph down to 5.8.

 

[Peat Phreak]

This will be more stable than RO. But if you still get pH drift, try 30% tap next time.

 

[Delps8]

So if i use hard tap water w a ppm of 450, it takes a substantial amount of ph down to get it in range.

If i use RO water w a 7+ starting ph, it takes… drops… of ph down to get in range.

Why?

Thanks in advance for your help.

This page on the BlueLab KB provides the answer, along with some background.

The key paragraph:

"As reverse osmosis removes all ionic and solid components present there should only be water present. The water molecules are made up of equal ratios of Hydrogen (H+) and Hydroxide (OH-) ions and so the pH should be neutral (7). However, as these ions are bound up in a water molecule (H2O) they cannot interact with the pH probe so you will not obtain a reading. High sensitivity probes can be used, but are a lot more expensive as they use a different technology, but these are not necessary for agricultural measurements."

 

[Phytoplankton]

I have tried to get that report online as ive seen other cities reports. Not easy to find or read what is available. I suspect it is high in iron bc toilets get a brown residue/deposit…. But not sure. If i can get the report i will try to post it

Got the same issue with my porcelain sinks, Iron and probably Manganese too,

 

[H20gro]

@Peat Phreak i have just discovered that my city was going through a “free chlorine conversion” process during my troubles. Are you familiar w this?

My tds ppm today is back to 150 range. Im wondering if the conversion from chloramine to free chlorine is what had my ppm up temporarily…?

Ive ordered another tds pen to confirm the drastic change, but am seeking advice on this process and whether i can now get away w tap as ling as it stays below 200 ppm.

 

[Keffka]

@Peat Phreak i have just discovered that my city was going through a “free chlorine conversion” process during my troubles. Are you familiar w this?

My tds ppm today is back to 150 range. Im wondering if the conversion from chloramine to free chlorine is what had my ppm up temporarily…?

Ive ordered another tds pen to confirm the drastic change, but am seeking advice on this process and whether i can now get away w tap as ling as it stays below 200 ppm.

Are you sure they went to chlorine and not to chloramine? Most cities are moving toward chloramine not away from it. Chlorine can be bubbled out chloramine not so much.

This may be irrelevant to your grow anyway since you’re hydro and I’m unfamiliar with the impact chloramine would have on hydro.

 

[bluter]

Because RO water has no bicarbonate to neutralize acid. You don't need to pH RO water unless you are growing hydroponically. If so, you can add some CaCO3 to buffer the acid.

you definitely have to ph RO depending on media and nute choice. same as any other water source.

@H20gro - don't screw around. stick with 100% RO unless you have good stable water under 120ppm. which you don't.
you can grow on tap without ph if you run LOS or other total organic approach. you could also probably run something like prescription blend without ph, but you'd have to match up your media and change your growing style.

 

[Peat Phreak]

@Peat Phreak i have just discovered that my city was going through a “free chlorine conversion” process during my troubles. Are you familiar w this?

They normally use chloramine. They are temporarily switching to chlorine for a few weeks. They do this because the bacteria count in the water got too high.

 

[LKABudMan]

So if i use hard tap water w a ppm of 450, it takes a substantial amount of ph down to get it in range.

If i use RO water w a 7+ starting ph, it takes… drops… of ph down to get in range.

Why?

Thanks in advance for your help.

Think of your water as a battery. The pH is the CHARGE on the battery. The ppm/tds is the SIZE of the battery.

Your tap water with 450ppm is a large RV-sized battery. You need to put a lot of power into it to charge it, but then it keeps that charge for a while. Likewise, you'll need a lot of pH up/down to change the pH on your water, but when it stabilizes it will be hard to change.

RO/Distilled water is the smallest battery possible. A little bit of power will charge the battery very quickly, but it doesn't keep the charge for long. One drop of acid in pure distilled water should bring the pH down substantially, but then one drop of pH up brings it up a lot, too. There is no buffering capacity at all, so it changes easily. Of course, adding nutrients to RO/DI water adds buffering capacity as well.

Finally, different salts (cation/anion pairs) buffer at different pHs naturally. So depending on the contents of your water, it will naturally want to go to a certain pH. Many nutrient companies use potassium salts to buffer in the 6.3-6.5 range.

 

[H20gro]

They normally use chloramine. They are temporarily switching to chlorine for a few weeks. They do this because the bacteria count in the water got too high.

Right, but do u believe this process would elevate the tds ppm and thats why it was 450? Now its reading closer to 100-125. Ordered new tds pen but this one is new too!!