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Old 10-23-2017, 11:06 PM
GpsFrontier GpsFrontier is offline
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Join Date: Mar 2009
Location: Lake Havasu AZ.
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Hello twd000,
The larger amount (2 tsp) is full strength for maxigro. As long as you know the manufactures recommendation for full strength nutrients you can adjust the nutrient strength to whatever parentage you want by simply adding or reducing the amount of water. If you mixed 4 gallons of full strength nutrients, and added a gallon of plain water you would have 5 gallons of 80% strength nutrients.

Don't get hung up on TDS/PPM/EC meters and values. Their a nice novelty to have around if you have money to burn, but don't really do anything worthwhile. In all the years I have been growing hydroponically I have never used one. Not only can they give you false readings, but cant do the only thing I want them to do.

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Would you recommend 2200 * 0.80 = 1760 PPM?
How strong I mix the nutrients would depend on many factors. Everything from the size of the plants, to the temperature and humidity, the type of plants, and probably even the size of the reservoir. Many more environmental factors will affect nutrient uptake even the amount of light and Co2 levels.

If I'm not familiar with a particular type of plant, that's when I may look at a TDS/PPM/EC chart. Not to try and mix my nutrients to the exact value on the chart, but to compare that value to other plants. That way you can determine if it's a heavy or light feeder, or somewhere between.

As an example: if I wanted to grow a plant and diden't already know I could look at the Vegetable Requirements chart to compare. You can see the recommendation for Lettuce is 560-840. when compared to all the other plants you can see the average on the high end is around 2100 to 2800 with some going as high as 3500. And the average on the low end is around 580 to 980.

Now if I wanted to grow Broccoli, with a recommendation of 1960-2450 PPM I can see it's on the high end, but not as heavy a feeder as some others. Remember temperature, humidity, size of the plant will all be considerations, but I would mix the nutrients closer to the full strength range. Probably in the 80-100% range. I would say unless the weather is hot, but broccoli is a cool weather plant and wouldn't do well in warm temperatures. Now if I wanted to grow Lettuce and a recommended PPM value is 560-840, I would probably only mix my nutrients to around 50%-60% strength because it's a very low feeder.

If I wanted to grow peppers I could tell from the chart their on the high end and a heavy feeder. I could also tell from the chart that sweet peppers aren't as heavy of a feeder than the hot peppers. Sweet peppers I would probably mix around 80%-90%. Regular peppers I would make a little stronger liken 80% -100%. If I were growing hot peppers I would probably mix around 90% to 110%.

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What are the signs of over- or under-fertilizing? I would expect yellowing leaves if under-fertilized...what about too much? Curling leaves?
Yes if you look at your plants daily and notice the new leaves coming out are a little yellow, assuming your pH is in range, then your nutrients are depleted. Yes curling leaves are a sign of your nutrients being to strong, usually curling around the tips and edges. But you may also notice the leaves suddenly become warped/deformed. If the leaves are dark green and otherwise look healthy but curling or warping, you'll want to dilute the nutrient solution.

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How do I know I'm near the maximum growth potential?
By observing your plants daily.. As well as providing them the optimum environmental conditions to reduce stress on them. That way they can focus on being healthy and happy rather than having to try and overcome hardship that will put stress on your plants.

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Will stronger solution cause faster growth?
Only if your nutrient solution was to weak to begin with, and if it was you would see yellowing leaves. If your plants leaves are healthy looking making the nutrient strength stronger will just damage your plants.

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Can I infer anything from the change in nutrient level in my reservoir over time? I assume young plants will be slow to take up nutrients. Not a lot of evaporation indoors.
Not really, again that's why TDS/PPM and EC meters are pointless to me. Sure over time the nutrients will become depleted in the nutrient solution, that's a given, and how quickly depends on how big the plants are compared to the water volume. Again common sense, no meter needed. Now if your referring to how quickly the nutrients become depleted after a nutrient change. The bigger the plants get the quicker the nutrients will become depleted. That is unless you increase the water volume as the plants get bigger. Think of it like a human. Will a little kid eat as much as a full grown adult? No.

That's why you need to design your system to hold enough water volume for not only full size plants, but have enough water volume for the total amount of water as well. As the plants drink up the water daily the nutrient solution will become more concentrated. The more the nutrient concentration fluctuates, the more stress on the plants. You want to replace what the plants drink with plain water. I always mark the inside of my reservoirs so I know exactly how much their drinking, and how much water to replace. I'll also sometimes add some diluted nutrients back to the reservoir to prolong the nutrient change.

Lastly the one thing I want a PPM/TDS/EC meter to do, it cant. It can't tell you what is in the water, much less how much of each element there is. It can only tell you the total volume. It can't tell you if there ate unwanted elements in the water. It can't tell you if your plants are consuming more potassium/calcium.iron etc. etc. Think of it like a measuring cup, you can pour a little of this in it, a little of that etc, at the end of the day it can't tell you what's in it much less how much of each, it can only tell you the total volume. PPM/TDS/EC meters are the same way. I can easily control the nutrient strength withough't a meter. What I cant do is tell what the balance of the nutrient in that solution is, and no meter can tell you that either.

Since plants use what they need and leave the rest, that means over time the balance of nutrients will change. You can add nutrients back to raise the PPM'TDS/EC meter values back, but since plants don't use them in even ratios eventually you will wind up with some elements reaching toxic levels regardless of what the PPM/TDS/EC meter reading is. That's why you do nutrient changes, to avoid the buildup of unused elements.
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