Soil Runoff pH, Flushing to correct lockouts- Why and how to do it!

[stinkyattic]

This is a common question that comes up when troubleshooting, so I thought I'd post up a little summin summin.

Why do you want to know your runoff pH? Simple- it's an indication of how your water, fertilizer, and grow medium are interacting chemically.

There are 3 measurements that are important to know when you are caring for plants growing in a soil or soilless medium.
The first is the pH of your source water.
Next is the pH of your nutrient solution after the fertilizers and supplements are added.
Last is the pH of your soil. But that's the hard one! You can't just stick a pH meter in the dirt and get an accurate reading, and the cheap metal-probed meters that show this are usually not all that precise.

So how does one determine soil pH accurately? With a runoff test! First, measure the pH of your tap water and record it. As an example, let's say that it is 7.0, exactly neutral.

Now place the pot over a clean rinsed container and pour enough water through the soil to start dripping out the bottom. Collect about 4 ounces of runoff water. Check to see if it is discolored as well.

Now, if you only have liquid indicator, which is just fine, pour this water into a clean small tube or the test vial that came with your pH testing kit.Add a few drops of indicator solution, shake, and read the color change.
If you have a meter, simply stick the electrode in the water and read.

Let's say that your runoff comes out at 6.5. How did that happen? The water passed through a more acidic matrix and dropped its pH. You can assume that your true soil pH is a couple tenths of a pH point lower than the runoff in this case- I'd assume about a 6.2. If it comes out HIGHER, just go in the opposite direction. If it came out 7.5, you can assume that you need to drop down from about 7.8.

You want around 6.0-6.5 for a soilless mix, or 6.3-6.8 for soil.

Pics:
1- Propping up the plant over a container to catch runoff
2- POuring clean water through the soil
3- For liquid indicator, pour into clean vials
4- Check the pH against the color chart
5- Adjust the flush water if necessary

stinkyattic Reviewed by stinkyattic on 04-07-2008. Soil Runoff pH, Flushing to correct lockouts- Why and how to do it! This is a common question that comes up when troubleshooting, so I thought I'd post up a little summin summin. Why do you want to know your runoff pH? Simple- it's an indication of how your water, fertilizer, and grow medium are interacting chemically. There are 3 measurements that are important to know when you are caring for plants growing in a soil or soilless medium. The first is the pH of your source water. Next is the pH of your nutrient solution after the fertilizers and Rating: 5

[Weedhound]

May I add something here? Well too bad......I'm going to anyway. I was talking to my hydro man and he told me about check PPMS of soil runoff........particularly valuable when flushing a plant or deciding whether or not a plant may need to BE flushed. Know anything about this Stinkster?

[stinkyattic]

Oh yeah, I forgot that. When I said see if the liquid is discolored, that's another indication that you might need to flush. You SHOULD measure ppms in a soilless mix, but usually if the pH is correct and you see lockout/scorch symptoms, you can tell that you need to flush. Most soil growers don't have EC meters. I've TASTED my runoff before to determine salt buildup- it definitely has a flavor all its own- salty, yet metallic! A fine vintage! :wtf:

[the image reaper]

wouldn't the fine particles of soil, etc., in the water throw off an attempt at a ppm measurement ? ...

[stinkyattic]

wouldn't the fine particles of soil, etc., in the water throw off an attempt at a ppm measurement ? ...

I'm going to say yes to that. Solids suspended in the water might not agree with your meter- if you want to test EC, I'd run it through a coffee filter first. But again, if it's soil, it's not really a big deal.

[Weedhound]

I'm merely a parrot here........my hydro guy says you can check runoff and determine IF you need to flush by the numbers (he says he usually will flush with a number around 900ppm) and then AFTER flushing he likes the ppms around 300 so Reaper you don't try to be as exact with it as with hydro. My understanding of this is that its much more for overnuting than ph in this case........but he SWEARS by it.

I agree Stink.....most soil growers DONT have e.c. meters to measure that stuff with. And while YOUR eagle eye (and eagle tongue ) may be able to see when something needs flushing etc....NEWB soil growers like me need all the help we can get.

[Mr. Clandestine]

Was it Hanna pH meters that have been getting questionable reviews? I found a Hanna pH/TDS/EC meter the other day on Craigslist for like $50, but I didn't call the guy because I thought I heard some bad reviews on Hanna products. Did I goof? Now that I've looked at some similar products online, it seems like it would have been a bargain, at least price-wise.

I'm trying to amass some toys for my trip into the world of hydro, but I have no idea what's reliable and what's not...

[sensilights]

so...if i'm using distilled water with a ph of 7 and add 1 tsp/gal of cal/mg which brings my ph down to 6ish (silly fish tank chemical ph tester is hard to tell exactly where its at) and my runoff measures at 6.5ish is the ph too low?

[stinkyattic]

I'm not a fan of Hanna, and my local hydro shop doesn't even stock them (the Oakton pH and Truncheon EC are apparently the best bang for your growroom buck as far as they are concerned).

6.5 is not too low for soil or soilless, but definitely keep an eye on it in case it gets any lower. I'm surprised that your distilled water measures at 7.0- generally, the presence of dissolved atmospheric gases (sepcifically CO2 and N2) will actually drop 'pure' water down into the 6's. You might want to get a 'second opinion' on your test kit!

Remember, for soil grows, tap water is perfectly acceptable in most cases!

[stinkyattic]

Add an airstone to your bucket that you let water sit out in, and consider a fish tank filter that accepts loose activated charcoal to run that water through recirculating for a couple days to reduce chloramine levels.

I found this about chloramine removal at home, and the rest of the article is a good explanation of the chemical and its use:

Drinking Water: Chloramines Water Disinfection in Omaha Metropolitan Utilities District , NF02-505

Chloramine Removal
Many water treatment techniques and equipment are used to alter and improve the quality of water. Several commonly used ones are not effective in removing chloramines. Worth noting are reverse osmosis and water softening units, neither of which effectively remove chloramines. In addition, boiling water does not effectively remove chloramines. And, unlike chlorine which dissipates when water sits for a few days, chloramines may take weeks to disappear. While sunlight and aeration help remove chloramines from water, allowing water to sit is not a reliable method of chloramine removal.
Two effective methods for removing chloramines include using a chemical to neutralize chloramine or using a granular activated carbon filter. Most pet stores sell chemicals for dechloraminating water and can provide use recommendations. Remember that chemicals that remove only chlorine will not remove chloramines. When using a carbon filter, ensure that it contains high quality granular activated carbon. Carbon filters should be operated at a slow rate to allow sufficient contact time for effective chloramine removal. Testing the treated water will help determine the optimum filtration rate. Filters must be monitored carefully to determine when the carbon media has reached the end of its useful life and needs to be changed. Manufacturers often indicate the maximum number of gallons that can be filtered before the filter is renewed. Check with the supplier for proper operation of equipment for chloramine removal.
A carbon filter also will remove chlorine, hydrogen sulfide, organics, THMs, some pesticides, and radon if present in the water. Unserviced or improperly serviced equipment may deliver surges of water with high levels of some of these contaminants. As the owner or user of a home water treatment device, it is your responsibility to ensure proper operation through monitoring, maintenance, and service.