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Originally Posted by jalayo  I'm new to hydroponics, and I have spent the entire evening, with no luck, searching the web for an answer to my question. I have built my own flood and drain system for tomatoes and peppers. I have a 45 gal reservoir and four 5 gal buckets and four 3.5 gal buckets. The plants are growing great and looking very healthy. I have run my nutrients for about three weeks. The lady at the local hydro store says to change them every 2 weeks. (But she is also the lady who sells the stuff). I have also seen that same comment (2 weeks) on this forum as well.
Today I got an ec tester and the reading for my nutrients was 1450. It should be higher for tomatoes. My question is how do I know how to mix my nutrients, so I can top off my system, so I won't burn/kill my plants? Is there any formulas that would help me calculate how I should mix my nutrients so I can top off my system and get my ec up to about 2400?
Thanks in advance. |
Well that is a good question, but has no good answer that I know of. I am not real familiar with the term "EC" meter but I am assuming that it stands for Electronic Conductivity and that would mean that it works on the same principal as the "PPM" meters (parts per million). It measures the level of electricity between two points to give a reading. There in lies the flaw in the answer to your question. Because the nutrients are made up of many elements (all of witch conduct electricity) it cant tell you exactly which ones to add. Plants drink up nutrients but they don't drink them up evenly. That is the plants will take up the elements they need at the time and leave others, depending on the plant type and phase of growing they are in.
Other than a $100,000 dollar lab machine I don't know of anything that can break it down and tell you exactly what is in the solution and to what concentration it exists. But that wont really help you anyway because Hydroponics nutrients come already mixed rather than in there individual elements. So you wouldn't be able to just add the ones you needed and not the others anyway.
Though with some attention to detail by checking the ppm/ec level along with pH levels daily, as well as keeping an eye on how the plants look, the meters can be very helpful. Also keeping an eye on how the plants respond when you change the nutrients is important. I would suggest keeping a log with all this information as well as any other changes that might affect the plants. I don't have any meters myself but I check the pH level daily. I have noticed that when the
nutrient solution is getting old the pH level starts to do some funny things, the pH also seems to be unstable when the nutrient temp gets to high.
I have had some conflicting information on this but it is my understanding that the more volume of water/nutrient solution per plant the slower it tends to go out of balance in general. I have read that Strawberry's need .5 litters per plant minimum. That would be for ten plants you would need 5 litters of nutrient solution minimum to feed them. With that you would probably want to change the solution once a week. Now say you were using 5 gallons of nutrient solution to feed ten strawberry plants, that is 4 times the minimum amount of solution. The math would suggest that the solution would go out of balance 4 times slower thus lasting longer. You would probably be fine at letting that go for 2 weeks. The ppm/ec meter can tell you just how fast the plants are absorbing the nutrients. I would expect the numbers to drop slower with the larger amount of nutrient solution. Even though it wont tell you what elements are being adsorbed by the plants, because of the larger volume of solution there is more elements overall to go around. Some plants are heavier feeders than others also.
I wouldn't go so far as to say, that simply a larger reservoir means that you don't need to change it because there are any number of things that can go wrong with the nutrients. But it is a factor in the equation. I have read about people who never change the nutrients but just add to what they already have, and I have also read about people who swear by changing the nutrients every week. Only careful observation will give you the best information. If you wanted to try just adding to what is already there I would just slowly add a little at a time, make sure that it is mixed well (Run it through a feeding cycle). Then test and see where it is at and keep doing it tell the ppm/ec numbers are in the right range. If it gets to high just dilute it by adding more water but pay attention to the plants for the best information on if that is working. If you have any doubts then just change the nutrient solution.
P.S. Some plants have different nutrient requirements as well as pH requirements. So growing plants with different requirements in the same nutrient solution can be a problem, though if your plants are looking healthy they probably play well together and will be fine.
06-20-2009, 01:44 AM
How do you top off your nutrients? 
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