General Hydroponics PPM Chart for Home Growers
General Hydroponics makes excellent nutrients, but their official feed charts are written for commercial growers running large, dialed-in systems. If you follow those numbers at home, especially in DWC or a small recirculating system, your plants will likely show nutrient burn before they finish their first week of veg. That’s not a product problem. It’s a calibration problem.
This guide gives you a practical General Hydroponics PPM chart built around real home-grow conditions. You’ll get stage-by-stage numbers, a clear breakdown of how to adjust for your water source, and answers to the questions that show up constantly in grower forums.
The General Hydroponics Flora Series (and What This Chart Covers)
The Flora Series is GH’s flagship three-part system: FloraGro, FloraBloom, and FloraMicro. Almost every GH feeding schedule and ppm chart you’ll find online is built around these three bottles, and for good reason. They’ve been around since the 1970s and the system works when you dial in the ratios correctly.
This chart focuses on the Flora Series used in recirculating systems like DWC, RDWC, and ebb-and-flow. If you’re running a one-part or two-part formula, your PPM targets will look different. If you want to convert EC to PPM, the math applies but the ratios won’t transfer directly.
PPM by Growth Stage: Beginner-Safe Ranges
These numbers are reduced from GH’s official chart by roughly 25-30%. That sounds like a big cut, but it matches what experienced home growers report as their actual sweet spot, especially in systems with less buffer than commercial setups.
| Growth Stage | PPM (500 Scale) | PPM (700 Scale) | EC |
|---|---|---|---|
| Seedling / Clone | 100-200 | 140-280 | 0.2-0.4 |
| Early Veg | 400-600 | 560-840 | 0.8-1.2 |
| Mid-Late Veg | 700-900 | 980-1,260 | 1.4-1.8 |
| Early Flower | 900-1,100 | 1,260-1,540 | 1.8-2.2 |
| Peak Flower | 1,100-1,300 | 1,540-1,820 | 2.2-2.6 |
| Late Flower / Flush | 0-300 | 0-420 | 0-0.6 |
These are starting points, not hard rules. Watch your plants. A plant running at 900 PPM that looks healthy and vigorous is telling you more than any chart can.
What I’d do: Start every new grow at the bottom of each range. If plants look great after 5-7 days, nudge up by 100-150 PPM. If you see tip burn or curling, drop back immediately. Creeping up is always safer than starting hot.
RO Water vs Tap Water: This Changes Your Starting Point
The PPM ranges in any nutrient chart assume you’re starting from zero, which means reverse osmosis (RO) water or distilled water. If you’re using tap water, you’re already adding PPM before a single drop of nutrient hits the reservoir.
Typical tap water runs anywhere from 50 to 400 PPM depending on your location. Some municipal water comes in at 200+ PPM right out of the tap. That 200 PPM isn’t plant-available nutrient at the right ratio. It’s calcium, magnesium, chlorine, and whatever else your water company adds. It reads on your TDS meter, but it’s not the same as FloraGro.
For tap water growers: Measure your tap water PPM before mixing nutrients. Subtract that from your target PPM. If your tap water is 150 PPM and you’re targeting 700 PPM in veg, you only need to add 550 PPM worth of nutrients.
For RO water growers: Start at zero PPM, but add a small amount of CalMag first. RO water strips out calcium and magnesium along with everything else. Without supplementing, you’ll see deficiencies even at adequate nutrient PPM. A CalMag dose of 100-150 PPM before your Flora Series keeps the ratios balanced.
If you’re unsure about NPK ratios for specific crops, NPK ratios for leafy greens are noticeably different from fruiting plants, which affects how you’d weight your Flora Series mix.
500 Scale vs 700 Scale: Which One Are You Using?
This causes more confusion than almost anything else in the hobby. When you buy a TDS meter, it’s calibrated to one of two conversion scales:
- 500 scale (NaCl): 1 EC = 500 PPM. Common in North America. Most GH charts in the US use this scale.
- 700 scale (KCl): 1 EC = 700 PPM. Common in Europe and Australia, and on many digital meters.
If you mix nutrients to 1,000 PPM on a 500-scale meter, someone on a 700-scale meter would read the same solution as roughly 1,400 PPM. Same water, same nutrients, wildly different numbers. This is why forum advice can be so confusing. Two people arguing about “correct” PPM for veg are sometimes just using different meters.
The fix is simple: know your scale. Check your meter’s manual or packaging. Then use that scale consistently and compare notes only with growers on the same scale. The table above includes both columns so you can use whichever applies to you.
Tip: If you’re unsure which scale your meter uses, measure a known solution. A 1.0 EC nutrient solution should read 500 PPM on a 500-scale meter and 700 PPM on a 700-scale meter. That test takes 30 seconds and settles the question permanently.
How to Read Your PPM Meter Correctly
A few practical things that matter more than people realize:
Temperature affects readings. Most meters compensate automatically, but some don’t. Cold nutrient solution reads lower than warm. If your reservoir drops below 65°F, your PPM reading will be off. Test at consistent temperatures or use a meter with automatic temperature compensation (ATC).
Test frequency matters by system type. In a recirculating system like RDWC, test every 1-2 days. Plants consume water faster than nutrients, so PPM drifts upward between top-offs. In a static system like Kratky, check every 3-4 days and top off with plain water when PPM climbs.
Calibrate regularly. A TDS meter that’s drifted by 10-15% is worse than not testing at all, because you’re making decisions on bad data. Calibrate once a month with calibration solution or replace the meter once a year if you’re running it hard.
For a deeper look at how to read and act on your readings across systems, understanding when to change your nutrient solution covers the full cycle, including when a reservoir reset makes more sense than adjusting.
When PPM Is Too High or Too Low
PPM too high: The first sign is usually tip burn on leaves, followed by the tips curling downward (called “the claw”). In severe cases, leaves yellow and crisp at the margins. This is nutrient burn, and it happens fast in warm reservoirs. If you catch it early, dilute with pH-balanced water and let the plants recover. Don’t flush and restart unless the burn is widespread.
High PPM can also cause nutrient lockout even when there’s plenty of nutrient in the solution. At very high concentrations, the osmotic pressure at the root zone actually prevents uptake. The plant starves next to a full buffet. Diluting the solution is the fix.
PPM too low: Plants get pale, growth slows noticeably, and lower leaves yellow first. This pattern suggests nitrogen deficiency, which is the most common result of under-feeding. Add nutrients in small increments rather than jumping straight to a high-end target.
A good middle ground: if you’re within 100-150 PPM of your target range and the plants look healthy, leave it alone. Chasing a perfect number when the plants are thriving is a recipe for over-managing.
FAQ
What PPM should General Hydroponics nutrients be? For home growers using the Flora Series, aim for 400-600 PPM (500 scale) in early veg and 1,000-1,200 PPM at peak flower. GH’s official chart runs higher; scaling back 25-30% gives most home systems a better starting point.
Are General Hydroponics feed charts too high? For commercial systems with large reservoirs, frequent monitoring, and optimal conditions, GH’s charts are appropriate. For home DWC or small recirculating systems, yes, they tend to run hot. Starting at the lower end of the range is the safer move.
What PPM for seedlings vs veg vs flower? Seedlings: 100-200 PPM. Veg: 400-900 PPM scaling up through the stage. Flower: 900-1,300 PPM peaking mid-flower, then flushing to near zero in the final week or two.
What PPM should I use with RO water? Start from true zero, add CalMag first (around 100-150 PPM), then bring up your Flora Series to hit your stage target. With tap water, measure your baseline first and subtract it from your target.
How often should I check reservoir PPM? Every 1-2 days in recirculating systems. Every 3-4 days in static systems. Always test before adding nutrients and after any top-off.
What is the difference between 500 and 700 scale? The 500 scale multiplies EC by 500 to get PPM. The 700 scale multiplies EC by 700. Same nutrient solution, different numbers. Know which scale your meter uses and stay consistent. You can also use a nutrient calculator to dial in your mix and cross-reference the EC reading directly.
Once you’re consistently hitting your PPM targets and plants are responding well, the next level is reading what the plants are actually telling you between tests. A hydroponic nutrient deficiency chart gives you the visual cues to catch problems before they show up in your PPM numbers. For a broader look at how PPM targets fit into a complete nutrient program, the hydroponic nutrients guide covers nutrient selection, mixing, and reservoir management from start to finish.