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# Lucas formula question

9 replies to this topic

### #1 Guest_steakandshake_* Posted 09 May 2012 - 12:03 PM

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heres a thread for the formulas page: Lucas Formula

I have a question about the lucas formula, specifically this method:

1. "Top off the reservoir daily using a pH corrected water solution as required to maintain full reservoir level. After adding back an amount of water equal to the amount of your reservoir capacity you should change the reservoir and put in fresh solution. "

So the bucket holds 3.5 gallons, and you top off with pure water with no nutes every day until you've put 3.5 gallons of fresh water in, wouldnt this cause the PPM to be too low? You dont replace the buckets NUTES until you have put 3.5 gallons of pure water back in, im thinking once you have put in like 2 gallons of pure water into the original solution (as time goes on and the plant drinks and water evaporates etc) you will get nutrient deficiencies? and the ppm will be quite below what it should be..?

very confused... (i did the lucas formula with the other method, topping off 100% every day and it really did not produce healthy plants)

I feel like im missing something....
OR is that what the addback calculator is for? says its only for advanced users though

Edited by steakandshake, 09 May 2012 - 10:56 PM.

### #2 Guest_steakandshake_* Posted 09 May 2012 - 10:58 PM

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Are you supposed to use the addback calculator every day to keep it at proper ppm nute strength?

Or is it correct that its supposed to go from say a full 950ppm (.5 conversion) then after some time, you've added say 2 gallons of pure water... this will bring the ppm down to like ~650ppm at least i would think...

### #3 Guest_steakandshake_* Posted 10 May 2012 - 07:55 AM

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some 1 set me straight

### #4 logistixz Posted 10 May 2012 - 11:49 AM

logistixz

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From what I understand when the water level drops that does not necessarily mean that the ppm levels will drop at the same time, the plant could just be taking in water in turn the ppm level will actually rise with the water level dropping. So no worry about ending up with low ppm water that will end up showing a deficiency of some sort because there should be enough nutes in the water for the plant regardless. Still a good idea though to change the water completely about every 7-14 days as the plant won't go through the systems capacity early in its life.

### #5 CasualObserver Posted 10 May 2012 - 07:39 PM

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S&S,

That your rez is 3.5 gallons, I am assuming your are in DWC buckets? If yes, it is recommended that you not use the addback formulas to try and maintain your nute levels at EC 2.0, but rather plan on dumping and changing every 10-14 days or after 100% clean water refill of original volume, which ever comes first.

I think you'll be surprised at how little the PPMs fall simply adding back clean water to equal the original volume (unless you have trees!). Water leaves the rez through evaporation and transpiration, but nutes are only taken up as needed, the rest remain in solution. If you do find that it falls to 650ppm, that would probably be a good time for a completely change, rather than waiting for your top off to equal the original volume, as you'd likely be having pH stability problems at that point.

In 3.5 gallons, you should be starting with 28 ml Micro/56 ml Bloom, preferably in RO water. If your tap water is below 300pm @ .7, or 214ppm @.5, you can probably get away with tap. But if you're near those upper limits, Hardwater Micro may be a better option.

Take a spin through the Ask Lucas Knowledge Base link in my sig. It's basically the Ask Lucas thread organized into various categories and stripped of all the extraneous posters. :-)

hope this helps!

### #6 Guest_steakandshake_* Posted 11 May 2012 - 05:24 AM

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Thanks guys! Clarified a lot for me

Yes i am doing DWC in bubble buckets. My previous grow was DWC in a 14gallon rubbermaid container with 5 plants in it. I ran into some yellowing issues and other issues, at the start i was using my ~260ppm @ .5 conversion tap water then i bought a RO filter and used that. These plants are trees, grew too big too quick, 4ft tall by 5ft wide, all in the one 14 gallon tub. I used the 100% strength top off everyday lucas formula method, without dumping the tub ever. Harvesting soon, alright bud for my first hydro grow, and i am definitely sticking with hydroponics for my flowering plants

Now I have 2 bubble buckets (much easier to work with) and going to try the pure-water add back method, where you dump once past the original capacity in pure-water. This seems to be the most popular method by far, dont see many posts about grows doing the 100% strength add back method. Hoping to get better results.

### #7 CasualObserver Posted 11 May 2012 - 02:45 PM

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Long time ebb/flow grower, but I'm a fairly recent convert to the Lucas formula and have become quite the student of his ideas and opinions. Although there are a number of reasons your last attempt could have gone south, the first thing that comes to mind based on your description is under oxygenated water. Lucas would have had you using a 4-5 watt air pump for your 14 gallons. If you've got one little pump feeding both your current buckets, check its wattage and bump it up to 2 per bucket if needed.

With the nute addback formula, you add plain water everyday and dose with only enough nutes once a week to bring EC back to 2.0, so if you were adding full strength nuted water every day, your pH likely dropped severely...eh whatever, that was then, this is now! ...just can't leave it alone, it's also possible that with such big plants, the bottom half of them wasn't getting any light. No light = yellowing, faltering parts. So the answer moving forward could be some pruning.

I think following Lucas' recommendations for pruning would benefit you and your two plant setup a great deal. When you put it under the 400 to veg remove the bottom three or four branch sets (they will wind up shaded and only produce fluffy popcorn), and top it at about the seventh set of branches so that you wind up with a candelabra shape of 3 - 4 sets of branches (which means 6 - 8 phat, sticky colas). If you can keep them to under about 8 sq ft, those 6-8 colas will be getting ~50 watts of light per sq ft...not the strongest, but not too shabby and if they're pruned to the nice even canopy as described above, I think you'll be very happy with the results!

Edited by CasualObserver, 11 May 2012 - 03:02 PM.
had confused OP with another's situation, removed reference

### #8 Guest_steakandshake_* Posted 12 May 2012 - 05:37 AM

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Thanks CasualObserver!

I had a ~3.5-4.5 watt pump for the first month of the grow then the second and third months i used a 14 watt pump

Yes I was adding 100% strength lucas nutes every time I would top it off, along with not having to dump the tub ever and refilll with fresh solution. I have a cheap PPM meter and I believe it got out of hand.

I will definitely prune much more next time, i did little to no pruning at all on the bottom of the plants.

Which method do you use for your Lucas growing? The 100% water top off followed with periodic replacement with fresh solution, the 100% nutes top off along with no replacing the solution, or the addback method? I need to choose one and stick with it , I have a good pH meter and a cheap TDS meter

### #9 CasualObserver Posted 12 May 2012 - 01:14 PM

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Then O2 in the water shouldn't be a problem! Keeping temps in the low 70s would also be preferable- below 72, really.

For buckets I think it will be best to addback clean, pH'd water until you've replaced an equal amount of the original volume, then dump and replace. If pH or TDS suddenly get crazy out of range, change the rez completely right then, but if the rest of the environment is in check, there shouldn't be anything too nutty going on. By adding back only fresh water and changing the rez as described, it won't be as important to have the TDS meter. Adding fresh water should raise pH, as TDS concentrates (from water evaporation and transpiration) the pH will lower.
I don't think we've mentioned what kind of water you're using? RO, hopefully?! If yes, you should be able to add full strength Lucas formula nutes 8ml/16ml per gallon and have pH come down, maybe to the lower edge of the desired range. You can adjust up to about the middle 5.7 - 5.8. As water evaporates, the pH should drift down, adding fresh water will bring it back up. If it dips below 5.1 - 5.3 you can add a little pH UP.

### #10 LiquidJunglist Posted 02 July 2012 - 08:35 AM

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Straight Vapor SON!!!