High Alkaline water, High pH and salt accumulation over time.
ganzigunnustarted grow question 14d ago
Previous grows with biotabs and blumat I always got rust spots and pistils turning reddish around day 40. I am thinking it's related to my tap water conditions. It has 140 mg CaCo3, 40 mg Ca, 6 mg Mg, 20 mg Na. It comes at 7.2 pH and raises to 8.2
im thinking epsom salt and ph-
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Green_Clawsanswered grow question 8d ago
The issue likely stems from high water alkalinity locking out magnesium and phosphorus, which directly triggers the classic rust spots and premature red pistils seen around Day 40.
Your diagnostic instincts are sharp. Tap water with 140 mg/L of CaCO₃ has high buffering capacity. Even if it starts at 7.2, that high alkalinity acts like a chemical sponge, pushing the root zone pH up to 8.2 over time. When the pH climbs that high, your plants can no longer absorb essential nutrients. Because you are using a Blumat system, the soil never gets flushed, causing those alkaline minerals and salts to steadily accumulate until the plant hits a wall in mid-bloom.
🛠️ The Strategic Battle Plan
The goal is to fix the water before it hits the soil, ensuring the Biotabs can do their organic magic without getting chemically blocked.
Objective Strategy Action Steps
Break the Alkaline Buffer Lower the input pH Use an organic pH Down (like citric acid or phosphoric acid) to bring your raw tap water down to 6.2 – 6.5 before filling your reservoir.
Balance the Calcium Fix the Cal-to-Mag ratio Your water has 40 mg/L of Calcium but only 6 mg/L of Magnesium (nearly a 7:1 ratio). Aim for a healthier 3:1 ratio by adding Epsom salt (Magnesium Sulfate) at roughly 0.1 to 0.2 grams per liter of water.
Reset the Root Zone Prevent salt buildup Once or twice during the cycle (around day 30, right before the trouble starts), do a gentle manual top-water break from the Blumats using properly pH-adjusted water to help redistribute sitting salts.
💡 Why Day 40 Matters
Mid-bloom is when cannabis demand for phosphorus (P) and magnesium (Mg) skyrockets. In an alkaline environment (pH 7.5), phosphorus binds tightly with your abundant calcium, creating an insoluble compound the roots cannot drink. This dual deficiency mimics a simple "underfeeding" problem, but adding more food only worsens the salt buildup. Fixing the water chemistry directly prevents this breakdown.
You have caught this early in the current cycle, and adjusting your water properties now will lay the groundwork for a flawless finish.💚
ZariRat_Growanswered grow question 12d ago
Hello friend, great grow, distilled water with pH 5.4 and in a couple of well-distributed waterings to the spot, good luck and happy growing 💚🍀🌱🍀💚
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MindFlowers68answered grow question 13d ago
I tend to have hard water around 350 ppm. A water filter gets my PPM's down to nearly 0 and my pH is around 7.7. If you're not using a water filter, definitely use one. That 20mg of sodium is gonna hurt in the long run. I don't use a expensive one either just a cheap carbon garden ones. Be careful with Epsom salt and having an already high pH because that will raise your pH even more. The cal mag solution I use, cal mag OAC from tps is slightly acidic so i use that to help ph my water down to 6.5. I noticed I used to have all these problems too until I started filtering, bubbling/aerating, my water, adjusting pH, and adding Calmag.
I'm really one of the least biggest fans of bottled nutrients, but sometimes it helps to have a few things when the plants have issues like a bottle of kelp and some cal mag can do wonders. I ran out for a few weeks, so I dissolved some gypsum pellets and Epsom salt and solution, and that seemed to work. Should work fine might take a little longer to act but if you get into a rhythm, the plant should respond well.
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Qutroanswered grow question 13d ago
Eyyy man,
I’d test the water alkalinity and the growing medium pH before adding Epsom salts or CalMag. A water pH of 8.2 alone doesn’t prove that alkalinity is too high. If the 140 mg/L CaCO₃ reading is alkalinity, it’s a moderate to slightly elevated level (about 2.8 meq/L), not extremely high, but it could gradually push the medium pH upward over time. If it’s total hardness instead, that’s a different measurement, so I’d confirm which one the water report refers to. I’d also check root-zone EC before considering a flush, and avoid adding magnesium unless there’s evidence of a deficiency. Reddish pistils alone don’t necessarily indicate a problem.
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RasendeRollo92answered grow question 14d ago
Hi,
Adjust your pH level and if it continues, give them CalMag. The symptoms indicate a CalMag deficiency, but this usually occurs as a secondary deficiency alongside a nutrient blockage.
Good luck 👊👍
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Nocone_Purpleanswered grow question 14d ago
Your idea makes sense. Your water has about 7 parts Ca to 1 part Mg, which is too Ca-heavy, and at pH 8.2 the soil can drift up and lock out Mg and other micros, which fits the rust spots around day 40. Adjust the water to pH 6.2-6.5 with pH down before each watering, and add a small amount of Epsom salt, about 0.25-0.5 g per litre, to bring Ca:Mg closer to 3-4:1. Check your runoff pH occasionally, and flush the pots with plain pH'd water now and then so salts don't build up. Hard water can also scale up Blumat cones, so clean them between grows. Watch new growth, and the rust spots on old leaves won't go away
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00110001001001111Oanswered grow question 15d ago
You shouldn't run into too many problems unless up near 500ppm and higher hard water. I have 300ppm water after the city's water treatment... well water around here is atrociously hard.
You may need a little more or less Ca than the next person, but that's just a matter of tracking how much you provide and trial and error until you get it dialed in. When i switched from tap to softened (lol, i know), i didn't have to change anything, and like i said, my water id 300ppm hard water with high Ca levels.
You might be better off running a soilless grow. The religious 10% runoff or more essentially makes buildup impossible... still possible to overfeed, but it will never be due to things building up in the medium.
Any acid will work well to balance it. Don't need the 20 dollar bottle of branded ph-down. White distilled vineagar (5%) is an excellent option most people can find cheaply at a local market. Can get 3gallons for 3-5 dollars around here. Probably 1-3mL per gallon to get from ~8 to ~6... again, just measure, test, measure test until you find the proper dosing.
pH after it's been added to pot can change because the plant doesn't not take in all molecules with water... so selecting intake leades to slowly shifting pH... again, another super power of soiless, the excess runoff built into the process will help reset that every time you irrigate.
don't add epsom unless you know it can handle more Mg and S ... otherwise you'll just cause an imbalance.
pistils can turn color even before day 40 of flower, so that's not too much of a concern and will vary.
While it might be a Ca issue, the picutres are a bit blurry... seems like some have chlorosis at the top, too... so you may also just be giving a bit too much light -- if it's minor it can take weeks to see symptoms. They get that crispy spotty look from that too.
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