Nutrient/ water usage

Rio_GrandeSeptember 11, 2013

I am back to this again.

I have about 30 gal in a partially buried 55 gallon drum.
The other day I brought the ppm to 830 and corrected the ph to 6.3
3 days later it was about 10 gal low. I refilled without checking ph or ppm, but after I checked it and the ph was 8 the ppm was 530
I corrected the ph to 6.3 then rechecked the ppm now it shows 380 ppm,

I checked and rechecked it several times thinking I may have goofed the first time. So I bring the ppm up to 580 but stop there because often if I let it run for a while the ppm comes up. I assume it takes a bit to fully dissolve.

Why would my ph and ppm swing so wildly.

I do have about 100 lettuce plants a week from being done then another 130 seedlings.
No doubt those mature plants are taking up both nutrients and water, but why the swing in ph and ppm when adjusting ph. I am using phosphoric acid as a ph reducer.

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PupillaCharites(FL 9a)


Can't be sure, but a couple of things to keep in mind is that you have lots of ppm in your source water that we don't know the composition. It is possible at higher pH you have something like Calcium carbonate precipitating out and effectively disappearing from the ppm, but when you acidify it, it redissolves. But then it rests and pH drifts up and reconfuses. Or depending on how you are adding the solid nutes, as you said they may not be dissolving well ... so wait an hour or so before adjusting the pH?

    Bookmark   September 11, 2013 at 4:56PM
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PupillaCharites(FL 9a)

Oh, I just remembered you are using a premixed powder that includes the calcium nitrate together with phosphates and sulfates. That couldn't be a good thing and insuring mixing must be a real beach and no doubt causing a lion's share of movements like this.

Mix your fertilizer in three parts next time you get more fertilizer. The recipe I gave nekbet in the other thread using the hydro tomato formula fertilizer plus calcium nitrate plus epsom salt gives a near identical nutrient combination as your 29 grams standard let use and is probably cheaper to buy (the only difference is the amount of calcium, using the 29 g 8-15-36 lettuce recipe it's around 111 ppm, and the recipe using tomato gives like 140 ppm of calcium.
post No. 20 of this thread.

This post was edited by PupillaCharites on Wed, Sep 11, 13 at 18:59

    Bookmark   September 11, 2013 at 5:07PM
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I will be to the point soon that I will order a bag of master blend and cal. I already have mag sulfate for the field irrigation.
I haven't been happy with the consistency of the mix. But it really just became a bigger issue now with the wide swings.

    Bookmark   September 11, 2013 at 8:30PM
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Rio - what nutrient formula are you using now?

I should get my masterblend and calc and mag tmrw or Saturday and am starting a new cycle of lettuce, kale and chard... I have a ton of pictures and data on the GH nutrients grow, so hopefully I can make a good comparison between them in just a few weeks...

    Bookmark   September 12, 2013 at 9:28AM
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Your lettuce is probably consuming more nitrogen than say calcium or potassium, thus causing your pH to climb. This will also affect the ppm as some elements affect ppm measurements more than others. I can't say which has more or less though. I just know they affect things differently.
The way i remember it is, pH swings indicate how well balanced your nutrient is and can also indicate what is being consumed more. ppm swings indicate whether your plants are consuming more water or nutrient.

    Bookmark   September 12, 2013 at 9:53AM
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I am using a mix from urban hydroponics, it is masterblend mixed with mag sulfate and calcium.

That makes sense grizz man. Part of this may be my fault. I have never mixed the nutrient to max strength. I may do that next week, clean the res and mix it per the instructions. If I follow the instructions I end up with 1000+ ppm and I just don't think lettuce needs that much. I want to maximize my fertalizer use and my lettuce growth. Just trying to make this as economical and productive as possible

    Bookmark   September 12, 2013 at 3:29PM
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I usually shoot for 600-700 ppm on top of my 300 ppm water.

Just dawned on me I may not be subtracting the 300 ppm from my final total. Some days I am dumber that a box of ...
The 1000 ppm might be right.
Now the question is try to add to what's in the resivour or pump out and start over?

    Bookmark   September 12, 2013 at 3:40PM
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Today's values, 600ppm and 6.5 ph. So ph rose a touch, but ppm stayed about same. The resivour didn't drop noticibly but it also wasn't 90 deg. So we may have just had a fluke. I need to bump the ppm up some. I have a line on the water quality tests that the municipality does regularly so I might not have to send one out.

    Bookmark   September 13, 2013 at 1:24PM
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600ppm with 300 base tap water? So only 300 of nutrients?

Do you have a pond water tester that will show you nitrates and some other values?

    Bookmark   September 13, 2013 at 4:15PM
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No but it sounds like something I need

    Bookmark   September 13, 2013 at 4:41PM
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PupillaCharites(FL 9a)

What Grizz described can be another problem, but it is not responsible for this particular quick and large ppm swing problem.

If there are 45 gallons and you are using the diluted lettuce blend you mentioned in the other thread, you're starting ~ 100-115 ppm N, especially since the plants were looking so good.

Your N ppm's for 160 plants of a maturity mix will drop between 6 and 12 ppm of N per day, probably 6-8pmm unless there are lots in the last week of maurity. After a little less than a week, the nutrient solution is ready to change in this example.

The relatively stable reading today and good quality of your plants, indicate the problem originally posted was caused by putting then Calcium nitrate together with the Potassium Phosphates in the fertilizer powder and putting that powder to dissolve together. Calcium phosphates then precipitate and the solution's ppm drops quickly, but as the system keeps flowing, the mobile calcium phosphates re-dissolve very slowly as they are spread around which reappears as large swings in the ppm, which swings back more quickly when acid is added, making adjusting hard.

    Bookmark   September 13, 2013 at 8:39PM
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Makes sense, is there a way to add back individual mutes or test for them? Otherwise this is gonna end up costing more than we bring in.

    Bookmark   September 13, 2013 at 8:51PM
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PupillaCharites(FL 9a)

You can submit your samples of your spent fertilizer solution to a lab if you want to after you get into a routine, and tweak the formula with individual additions, but that is almost definitely not worth the effort with the formula you are currently using because it is specifically designed for lettuce use already and what you just need to do is make sure your water is good and fix the way you mix up the solution.

Each week per 160 plants you need to run through like less than a lb. of powder for the three components. Multiply that by 5 weeks, just call it well under 5 bucks a week, that's $25 ,max in nutes per 160 plants, or 16 cents a plant plus the pH down. Check your own numbers more exactly but you might find it even less.

If there is a solution problem out of whack it is usually preferible to just change the whole thing and reset everything back to normal in a situation like yours where the non-nutrients in the source water keep accumulating and the plants will appreciate a change as well.

But to save some good cash consider a nursery and mature separate section when you outgrow the current pump capacity. Then in the nursery (after transplant from seedlings if you are doing it like that), the first like 10-12 days at 2/3 strength ought to be overall better for the plants and your wallet, and if you could cycle, and in the mature section maybe weekly, keeping in mind that a lettuce bulks up about half of its final weight in the last week or so.

You're already making some nutrient additions sometimes when you top off which is an efficient use of the blend the general idea o get everything out of the nutes you can before tossing them. Just guide yourself by the idea that each lettuce sucks up around 5 grams of fertilizer to maturity and if you do it right you will toss out in changes less than another 5 g on all the solution that got spent in its life per head.

BTW, I thought I never would grow lettuce and you just got me hooked ;). But fisrt to finish the strawberry NFT, my plugs arrive in 5 days oh crap, see y'all in a week unless I have a problem and then please help (shameless plea now that the pressure is on)

This post was edited by PupillaCharites on Sat, Sep 14, 13 at 3:25

    Bookmark   September 14, 2013 at 3:21AM
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Lol, lettuce is tasty.

Interesting today, resivour dropped 15 gal since last top off but the ppm only changed by 100 and the ph only incresed 1 point. I am not sure how to interpret that?
I added nutrient to take it up to 750 this time as some of the plants don't look as good as they have in the past. Added water and finally adjusted the ph.

    Bookmark   September 15, 2013 at 3:29PM
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PupillaCharites(FL 9a)

LOL is right, I never was a lettuce fan before but having big plants from starts in a month feeds some childhood fascination about watching plants grow.

Because your water is pretty hard you need to really get an analysis done on the hardness composition. The only thing it sounds like is that your plants ran out of enough food strength, the formula is working fine and you're maybe even mixing more carefully, and everything is dissolved like it's supposed by now.

I just noticed you said you only had 30 gallons in the res. I was thinking you had a 55 gallon drum but then I read the original post again and you say only 30 gal. That is way too little. The plants are going through it quickly. I have no idea what commercial growers use but for weekly changes of maturing plants I would be uncomfortable with anything less than 60 gallons (but not too much more to save on nutes), just based on the data you are sharing.

If you are using say 25 grams per 5 gallons for example look at it this way. If your water is 500 ppm, those 5 gallons have 10 grams of something else in it already, so by the time you change out a quarter of it you have the same ballpark of crap in it as fertilizers and the EC starts to make you think your nurtrient is still pretty strong when it is unacceptably weak. It also sounds like the average age of the plants is bigger so for sure don't economize on the 29 g per 5 gallons any more since you have a bunch of real hungry big girls to feed.

    Bookmark   September 15, 2013 at 5:43PM
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Makes sense and I have been playing with the mixtures considerably in an attempt to be as cheap as I can without letting the plants suffer. I can fill that 55 gallon drum up, I have just been filling it to the top line and guessing that is 30 gallon. I can even bury 100 gallon tank that I have, but I would like for this system to run on the 55 gal drum as I have bigger plans for the 100 gallon tote.

I am going to either order a bag of masterblend this week, or I have another complete nutritent that we use in drip irrigation that looks promising for the hydro. We add Epsom salt to it and send it to our dirt born plants.

Everyone here knows my parents are farmers. Mom does alot of cut and come again but these plants were grown for heads. We used 3 or4 ugly ones to make a big salad this week and when I came over today she had put the stalks back in the system and you know,,,,,,, we will be pulling leaves off of them soon.

    Bookmark   September 15, 2013 at 6:14PM
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PupillaCharites(FL 9a)

Rio, ok you say the water is 300 ppm. even though you should have a ~70 gal res (per 160 maturing plants) which would let you change after replacing 50% of the water or so. If you still have 30 gal, maybe this schedule can be helpful:

30 gallons res with 300 ppm water for *accumulated topping off* ppm targets.

topoff nute water target ppm
0% 700 300 1000
5% 700 315 1015
10% 700 330 1030
15% 700 345 1045
20% 700 360 1060
25% 700 375 1075
30% 700 390 1090
35% 700 405 1105
CHANGE ME (when about 22 gal are left)
if instead you want to keep going to test your economy:
40% 700 420 1120
45% 700 435 1135
50% 700 450 1150
55% 700 465 1165

even though some of the water ppm will be used by the plants, your formula already has a decent amount of Calcium and Magnesium in it, but this smaller detail will be offset by excess phosphorus from your pH down, which will also add to the 1000 ppm start point, depending on how strongly the water is buffered toward higher pH.

This post was edited by PupillaCharites on Sun, Sep 15, 13 at 18:52

    Bookmark   September 15, 2013 at 6:28PM
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Thanks, I will copy that and hang in the pump house.

I will have a more accurate measure of how much water is used soon, we have been discussing getting a in line water meter for the other irrigation system. If I do that we will make it removable to use when filling fresh tanks.

Next weekend we are going to empty the system and recharge the nutrient. We are supposed to have rain this week, so I am going to try to catch some for refills.

    Bookmark   September 15, 2013 at 8:30PM
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PupillaCharites(FL 9a)

Sounds great. Those numbers are approximate but it's a heck of a lot better to have a guide than flying blind and when things stabilize you can hone it down better. If you use all virgin rain for the refills of couse you just keep it around 1000 the whole time (making the initial solution with farm water, and using rain for refills only) but you still do want to do the change because of whatever undesireable plant and microbe wastes, and sometimes even stuff like copper from the fertilizer itself start accumulating. Same with parti

If you can add a 70 gal total res then change time becomes a standard change after 50% is refilled instead of 35%, at first guess, so really using a smaller res doesn't save much and might be taking some of the fun out of it because all the changes are being concentrated and magnified in a little water.

I wasn't thinking of getting fancy, just adding whole amounts of a measured amount like by a two gallon container or if you size the res bigger, like marking a level in a 5 gallon container and just keeping tally marks on a pad one page for each cycle (like, 3.5 gallons which is also 5% of 70 gallons and would go good with the chart above). That way when you skip adding nutes because it looks ok you can always pick up where you left off when adding fertilizer in water to top off.

    Bookmark   September 16, 2013 at 12:02AM
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That makes sense. I have an idea that will buy me some maintenance time. I may place a 55 gal on top of the ground and put a hose between with a float valve in the main tank. When the water drops that will automatically fill the main tank. If I start it all out together close to the same values will it work? Or will it just mean more unwanted ppm?

    Bookmark   September 16, 2013 at 12:47AM
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PupillaCharites(FL 9a)

If I understand correctly (which I may not), that will not help except to automatically fill in case you aren't checking on it. At the moment I don't think you can leave your system without checking on it to trust auto topping off.

But if you want to do an auto topper off-er, be sure to put half strength in the backup topper off source (or whatever the ratio is that has been working for you on average temperature days). The crap ppm problem will continue in that design, if only the small res is being mixed and recirculating.

If you want to do a Rube Goldberg fix, in that design, have the return water fall into the new above backup, not main, one and then have the pump in the main buried one with your auto refill design (and you still need to keep it topped off). Maybe that's what you meant, not sure, if so sorry for not following, but if you can work the levels to continually drain from upper (where the return falls) to lower, and pump out of lower, pull this idea of off it will work.

Don't worry about mixing in that last example. As long as there is a continuous flow from upper to lower the nutrients will mix well enough all by themselves. Mixing helps but nutes already in solution will be all over each other like stink on a monkey (Seinfeld reference).

    Bookmark   September 16, 2013 at 3:05AM
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PupillaCharites(FL 9a)

If you dig another %$&^&$ hole and put the two drums at the same level, all you need is a siphon hose securely fastened deep between the receiving drum and the pumping drum, prime the hose, putting the pump as far from the siphon inlet flow as possible and it will be ok, as long as the hose is thick enough it doesn't clog.

    Bookmark   September 16, 2013 at 3:13AM
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