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Nutrient Readings

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I have read two different ways of determining nutrient strength using a Truncheon or any meter and I want to know which one is correct.


Most nutrient labels say that the nutrient strength shown is in addition to the water ppm. In other words, my water is 210 ppm if I want a ppm of 1200, do I mix it to that and add to the water. That would give me 1410 ppm or do I mix nutes to 1000, that would give me 1210 ppm.


I read an article that said to deduct 50% of the water reading from the total ppm reading. In other words, if I mixed to 1200 and deducted 50% water reading, I would have 1095 ppm.


I find this confusing as I am using low strength nutes (1/4 strength) on my 50 mm high seedlings and have been told to use around 400 ppm. The reading I am getting is 700ppm so if I deduct the water, I have 490 ppm. If I dont, I am overfeeding them though.


Please advise

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No truncheon or E.C. meter can measure ppm. It's impossible. It's just a convenient way to convert the e.c/cf reading into ppm, which varies from country to country... (that should give you a clue as to how scientific it is. :) ) E.C. or C.F. is much easier to read and determine where your levels should be, IMO.


Now, as to the water. The water you use will contain various proportions of minerals, depending on where you live. If it's reading too high you could consider some kind of pre-treatment, but it's not really necessary unless you're on bore or similar water. You should be aware that whilst the minerals give a reading, they're not really that nutritious to the plants. The water out of the tap can contain all kinds of stuff, but most of it isn't used. So your friend has given you some reasonable advice, vis a vis halving the base e.c. and subtracting that from the total e.c. to determine tru levels....


But why bother? It's so much easier to just set them up with a 1/5 or 1/6 strength nutrient, (some growers use 1/4 but around there's fine.) see what the levels are, and use that as your seedling mix. As the plants grow, you'll be able to tell if they're at the correct levels by how the plants leaves appear and react to the feed. If they burn they're too high, and if they go yellow they're too low. It may take a few seedlings deaths for you to work out what's what, but there are plenty of links in the grow faq here to help you identifying nutrient deficiencies and toxicities.... Aaaaaanyway, as the plants grow, you'll need to slowly increase the nutrient concentration to support them. I usually make it a point on the truncheon, or .2 ec/2cf each week of growth. But it can be less often, like a fortnight, depending on clones/seed/temps/ and a few other factors.


The nutrients will have to be dumped and reformulated at least f/nightly, preferably weekly. This only really applies tho if you're using a recirculating system, as a run to waste can be run simply enough without having to dump the nutrient tank at all, as you'll be adding the same water and nutes at the same concentrations... If it's kept dark and stable it should be fine, and easily adjusted up or down with water or more nutrients. But if you've got a recirc system or a run to waste, you'll need to do a flushing. This means running fresh, ph adjusted water through the pots several times, until the e.c./c.f. levels of the water draining out are the same or only slightly higher, (like 1 or 2 points at the most) as the water going in. This could take several watering cans per pot. Try not to flood the pot too much, so as to avoid disturbing the roots with the media floating around everywhere. This flushing is done to clear the system of excess nutrients which collect on the surfcace of the media as the nutrient is passed over it. If it's not done, the plants will progressively get more and more nutrient, and start to suffer because of it. So flush weekly.


On the factors affecting the e.c. you'll want to be at for your plants, well, there are a few general rules you can follow to assist in giving the best to your plants. Make sure the water temp is stable at 20 - 26, with 23 being about the ideal. This ensures a good oxygen holding capacity, (an air stone in the res is a good idea too) in the water, as well as making for a nice temp for the nutrients to be absorbed out of the water. If the water gets too hot, you'll be susceptible to problems, likewise with too cold. It's easy enough to keep it warm, you just get an aquarium heater, set it and ensure you never run dry in the res... (a float valve and second feeder reservoir is a good idea for this) this will keep the water at a good temp with little maintenance. Keeping it cool is pretty easy as well, although it may take a bit of experimentation. Just freeze a couple of bottles of water, and then use these (with the lids on of course) in the reservoir as a coolant. Once it's reduced down to water in the bottle again you can swap it with the second bottle in the freezer. This could be as often as daily, or more if the temps get out of control. How big the bottle needs to be depends on the size of the body of water. More water means you need more volume of ice to cool it. :)


As to temps in the growroom affecting nutrient needs, there are a few tips there too. Higher temps mean you should lower the nute concentration slightly for optimum growth, and cooler ambient temps mean you'll need to slightly increase the concentration. Humidity and air flow also affects this. You'll find some more detail in the growfaq.


As the nutrients are drawn from the reservoir by the plants, you'll notice the e.c. going down slowly, and the ph rising. This is natural, and something you can plan for. (All this applies only to recirc btw) By using a feeder reservoir to provide fresh water to the nutrient reservoir, thus keeping it at the same level, you'll be able to accurately determine the concentration of the nutes in there. If you were to not top up the nutrient res, even with nutes being used by the plants you'll end up with a more and more concentrated solution. This could be a disaster, so you can either regularly check and manually maintain the levels, or set up a feeder res. The pH levels can be kept more stable with a feeder res too, as you can maintain the ph level in the nutrient reservoir by keeping the feeder res slightly lower in pH. I keep mine at .5 below my nutrient reservoir, so 5.0 or thereabouts. My nute res is therefore kept at 5.5, as even tho nutrients are being removed from the n.r. which is raising the pH level, you'll have slightly lower pH water being replaced into the n.r., thus keeping the pH levels more stable. Of course you can't judge it perfectly, this is a living plant we're talking about, and all kinds of things can happen, but the more stable you maintain ph levels the better the plants will grow.


Nutrients are being pulled out of the n.r., so the e.c./c.f. is going down. This is easily fixed by topping up the nutes again, right? Well, yeah, but you won't really know what's in there. Plants absorb nutes at varying rates, and use more of some at different stages of growth and less at others... So the recirculated nutrients are no longer balanced after a few days, even tho they still contain good nutrients. So how do you fix it? Well, you can top up with nutrients, but you should only ever do this once in any given cycle, and it shouldn't be more than half of the original amount of nutrient you've put in when you initially set it up. So if you've used 40 ml of nutes in your res and you're e.c. is dropping slowly over the two or one week period between dumping, then you shouldn't add more than 20ml as a top up to that tank. It's usually much easier to just not top up the nutes in the tank, as if you don't keep good records you can quickly forget what you've used and how much you can add... and even then the guide I gave you then could very well over fertilise the plants in one nutrient. So just let the e.c. drop slowly, in which case you'll want to dump the nutrient res weekly, particularly when the plants really get growing, as they'll be using craploads of nutes... trust me on that one.


Whew... can you say RSI? Ouch... Anyway, I hope this little spiel has helped ya, if you check out the growing faq's and use the search function you should be able to find some more information on the subjects above in here... Nutrient management is nowhere near as complex as I think I just made it sound, it's quite easy to know what you should be doing in the end once you get into the groove. Take your time, learn about it and ultimately practice and see what happens. If you find something works for ya, use it. If it's causing you problems then critically analyse all you've done and try and pinpoint the cause. You can fix most nute problems with a flush and reformulate, but not always, so it pays to check out all you can. Try and provide a stable environment for your plants within the ranges they like, and you'll be laughing. Good luck, and may the Force be with ya. ;)

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mate, PPM is a conversion of EC. Thats whats great about Truncheon, it gives you EC and PPM readings simultaneously. but, I know what you mean, its hard to take advice off people talking in PPM when your meter reads in EC. Well, in Australia, 1.0ec = 10CF = 700PPM. But the ratio is slightly different in different parts of the world. check out the FAQ at www.overgrow.com if you want to know the conversions in other countries.


and yeah, you mix nutes with water to a strength, the base EC of the water is irrelavent in this calculation. by measuring the mixed solution you are automatically taking into account the base EC of the water.

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Ok guys how about this one.


I have 15 seedlings about 35mm high in rockwool cubes sitting in expanded clay in a recirculating system. They have been there for 5 days.

When the reservoir was filled with 30 litres of water, nutes were added at 1/4 strength (37.5 mil Dutch Master Advance) according to label. pH was adjusted to 5.5 . CF reading was 8.

Each day I have had to adjust the pH as it climbs to around 6.2. The CF changed 2 days ago to 10. I have just checked it again and it is now 11, the pH is still 5.5.

Is it possible that the algae which has accumulated on top of the rockwell cubes is responsible for the CF rise? If so, should I cover them with some of the expanded clay to keep the light out.

The only other additives in the tank are Oxy Plus and Phytoff.

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No, as the solution level decreases (from evaporation and perspiration) the nutrients remain behind in slowly increasing PPM. The nutrients used by the plants is neglible especially in the Summer over one week. I found I used over 10ltrs of PH balance water to top up my 70ltr tank in a week.



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