High soil pH in discharge water

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I’m not quite understanding what you are asking.

If your soil pH is really high, it might because the water you water your plants with also has a high pH and also maybe a very high level of alkali dissolved solids, also known as “hard water”. These alkali minerals, like “lime scale”, can continue to build up in your soil and bring the pH way up.

You need to get a report of what is in your tap or well water to find out what exact minerals are dissolved in your water, but you could also get a reading with a digital EC/TDS meter and you can also get a pH reading of your water with something like this combo:


Hi MacG, the pH of my in going water is checked with each watering and is consistently adjusted to 6.2 - 6.5 pH. My water from the tap sits for a couple days before feeding my four White Widow ladies. It’s TDS is low, around 180 and pH right out of the tap is 7.0. I am at day 42 of flowering and my leaves above my SCROG are yellowing big time. The pH of my discharge water is 8.2 presently. I am using Roberts Boost nutrients. Also, the seeds are from ILGM. I am happy to answer any questions that will help my grow. I had added the recommended amount of Dolomite lime before planting in 7 gallon cloth smart pots.

TDS of 180 isn’t actually low. 50 or below would be low, but yours is far from the highest I’ve seen. I suspect the bulk of this TDS is from a lime stone like mineral and likely to contribute towards a high pH in the long run.

The dolomite lime might be the culprit, this can bring your pH up a lot.

Dolomite lime is usually recommended to be added to a soil mix that has a lot of organics that will decompose and acidify, if you don’t have this acidification going on to balance with the alkalinity of the lime, your pH will likely climb up instead of staying steady near more of the 6.0 - 6.5 range.


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And so it sounds like you are going to need to flush with water that is maybe adjusted as low as 5.5, and flush until you get your pH coming out at nearer your desired range. You can flush with 3 times the volume of soil with properly 6.2-6.5 pH water, but you might need it a little lower to get you soil’s pH down to where you want it. And then water/feed once with properly pH and nutrient mix to replace everything that was flushed out.

Also, at day 42, maybe you don’t want to add too much nutrient back in the soil, This would have to be a judgement call by your own time-frame and feeding concentration throughout the grow.