The Lucas GH 3 part formula

This is for JW and WH and any others who are not familiar with this GH 3 part formula which is a widely used and respected feeding chart for the GH 3 part.
From the OG FAQ
Reposted by BlueBear Nov 17, 2006
General Hydroponics Flora Series Feeding Strategy - Lucas Formula

G-M-B (Grow-Micro-Bloom)
0-5-10 - For Vegetative cycle (18/6)
0-8-16 - For Flowering cycle (12/12)

The numbers above indicate the number of milliliters (ml) of Flora Grow, Micro or Bloom formulas that I use in one gallon (US Liquid) of nutrients.

You will notice I dont use any of the Flora â??Growâ?� formula, do not need to, the Flora "Micro" provides plenty of Nitrogen.

There are two ways to work with this formula:

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.

2. Top off the reservoir daily using a pH corrected 100% strength nutrient solution as required to maintain full reservoir level. Continue to use this nutrient
solution without dumping the tank unless the PPM rises above acceptable levels.

Between vegetative and flowering cycles you should dump your nutrients, then flush (possibly with Clearex) to remove salt buildups, then change to the other
feeding program. Always shake your GH nutrient bottles before using them!

For young plants, just transplanted into the hydro setup, give them 50% strength nutrient mix to prevent overfeeding them while their young. Gradually bring
up the mix to full strength as they grow over the next few weeks or so.

The lucas formula is normally intended for use with RO or near 0 PPM water.

NOTE: The Lucas formula eliminates the need for Epsom salts to correct (Magnesium) Mg deficiencies in most normal feeding programs recommended by manufacturers.
Cannabis needs a lot of Magnesium to thrive.

The Flora Micro is providing the Nitrogen and the Magnesium in the proper balance, thus there is no need for the Grow formula and little or no room under
the maximum acceptable ppm limit of 1600 @ 0.7 conversion.

Calculated EC/TDS levels:

EC microsiemen:
0-4-8: 946 µS
0-5-10: 1184 µS
0-8-16: 1894 µS

TDS @ 0.5 conversion:
0-4-8 = 473 ppm
0-5-10 = 592 ppm
0-8-16 = 947 ppm

TDS @ 0.7 conversion:
0-4-8 = 663 ppm
0-5-10 = 829 ppm
0-8-16 = 1326 ppm

Addback Calculator - (For Advanced Users)

Say you were running the 0-8-16 formula, at 0.7 conversion with a 22 gallon res. When you first fill it up, your ppm will be around 1330.

Now you have been growing for a week, and some of the water has been taken up by the plants, some has evaporated, and now your res is at 947 ppm. You need
to get your ppm from 947 to 1330. Here is the equation:

((target - current) / target) * 8 ml per gallon * res gallons = Flora Micro (ml) double this figure to get Flora Bloom (ml)

Example:

((1330 - 947) / 1330) * 8 * 22
(383 / 1330) * 8 * 22
0.3 * 8 * 22 = 53 ml Flora Micro

53 ml Flora Micro, double that and you get 106 ml Flora Bloom. So 53 ml Flora Micro and 106 ml Flora Bloom to add back to your 22 gallon res to get you
from 947 to 1330.

Using Hard Water GH Micro

I had been experimenting with using the Hard water Micro as a substitute for the normal Flora Micro, this to account for my hard 350 PPM water and the lack
of a large enough RO filter at the time. It has worked well for me. I just kept my reservoir below 1150 PPM @ .5 conversion and its all good.

One tip - do not pH down this stuff, the hard water micro will drop pH gradually over the next 24 hours, for example I mix up a batch, it is at like 6.2,
the next day, its at 5.6-5.8 after running in the system for a while. If I pH downed that to 5.7 before putting it in the system, it ended up as low as
4.8-5.2 by the next day.

My conclusion, the hard water micro was buffering the alkaline crud in my water, it just doesnot do it ASAP fast like the phosphoric acid.

Bear I cannot thank you enough for posting this but I'm afraid I do not for the life of me understand the conversion thing etc... Allow me to study this entire thing for awhile and I will return with questions; probably about nine million of them. I want to try this 3 part thing but also want to understand it before I do. Where exactly does the Cal Mag fit into this equation? You said it was a must for you; and what else do you add to this? Lk?

I just tried a version of PIF's solution to adjusting ph daily and it worked great for me--involves rotating the solution daily, pumping out the stuff in the individual buckets and returning it to the top rez allowing the fresh in already ph correct. Can this method be used in conjunction with this? Again thank you so much for posting this...I will study up so I can try it.

PS JW--I tried the above on PIF's theory and it really did the trick...no lifting the buckets out etc. I ended up throwing some of the solution away as I could see small bits of root and crud in and added put in some fresh....I DID NOT HAVE TO CLEAN MY DRIPPERS TODAY. I am in heaven!!! Thanks PIF.

To start off the 3 part formula works best with RO water or tap water with a low ppm under 300 I want to say, maybe a little lower. The Cal Mag should really always be used when using RO water or water with a low PPM, you see the RO process can cause the water to loos some of the natural micro nutrients that are in water that MJ needs and without those micro nutrients MJ can show defs in certain areas and the Cal Mag provides those micro nutes so the plant can still thrive andbe be able to have a healthy life cycle. So the answer is yes the Cal Mag can work in conjunction and I just explained the need for it.
When you say that you don't understand the conversion table, which part are you referring to? The EC, Calculating for advance up types, basic feeding or what. Once you understand the basic idea of veg and flower according to PPM/TDS I think it becomes much easier. As for the Pith, I am not sure that you would need it with the 3 part for the fact that the 3 part has PH buffers that are pretty consistent.
Well, don't feel obligated to try it, just think about it and if it isn't going to be something that makes you or breaks you for some certain reason and you feel comfortable then give it a run.
PS, I am sure that there are some people on here that have exp with it, as a matter of fact I think that Lake Wood or GK use a modified version. Also just like most formulas people have their problems or tweek it a little to fitt their likes, while others just look at it like a god send.
Adieu

Looks like Lakewood or GK could have some input too. This is how I am approaching my add backs. Tell me if my Mode of Operation is flawed?

I set up my resi and wait for water to go down. I add back with full strength solution. I am changing out my resi every 2 weeks. I have been instructed by the person selling me the nutes to replace the solution weekly but in an effort to save time and dough I am experimenting with twice a month.
I am set to do my first resi change in the flowering period tomorrow. Things seem to be ok. I noticed a bit of what I reckognized as a mag deficiency so I did toss in some extra cal-mag at 10 days.
I noticed that in the lucas method it is suggested to let the resi go until PPMs are raising too high.
I don't like this thought because I know that some nutes will be used more than others and the balance will be thrown off more and more.
I guess the threshold of ppms lined out will keep the solution from becoming toxic but I am afraid to run an experiment and have my grow get jacked.
Anyone out there using a full strength add back routine? I would love to hear a voice of experience.

Thanks guys, -Jay

Well you are saying exactly what I am wondering---I do change my nutes once a week and sometimes if I see a problem and it always seems to give my plants a kick in the butt. I am wondering if there is more to this which is why I would like to study it further--I am definitely getting the impression that it is worth the extras it causes because I hear about them over and over and bigger plants etc would certainly be worth it. Ph staying more stable I like. Questions I can think of right now would be what percentage Cal Mag w rO water vs nutes (I go 50% now vs nutes)and is there a formula or something for increasing the nutes as the plants grow. And I hav always gone by ppms vs EC because I don't really understand it. AND am I correct in thinking TDS and PPM's are the same. Many ???s Must study.....

Oh, you guys are going to make me think, unfortunately I have to get my baby for a little quality Poppa Bear time, but first CJ some do add backs your way and you are right about the possibility of problems arising when waiting for the PPM to rise when doing add backs, but your hydro system can play a significant role in the way your helpful/positive bacteria deal with that process, for instance in the Bio Bucket hydro set up it is set up so you should not have to do a ress change throughout an entire grow because with the level of aeration and the positive bacterial cultivation off setting and balancing out the problems with negative bacteria, PH problems and other complex things that take place with the rises in PPM which in that particular system are combated by a good strong bacterial environment.
For weed hound, and Cali J the larger the res generally the more leeway and flexibility you have with PH and PPM management. For WH PPM and TDS are the same and yes there are charts that help to rays the PPM throughout the grow, but sometimes this is strain dependent regardless of the chart, for instance something like White Rhino will be able to handle a lot less then a strain like Skunk number 1 where I could feed it all day and it wouldn't flinch and this strain I have now burns at anything over 1000 PPM even at the latter end of flower.
Wish I could of popped all of the answers out, but some answers need a little preparation before a understandable explanation can be given and also I have to try to tighten up the screws on some of the information before I try to explain more, all answers can't always be off the cuff responses.
Adieu for now.

Well mine always are--that's why there's no real information in them. Besides Bear if you answered them all right now I wouldn't understand them anyway. Need at least a basic floorplan before I'm sure what to ask...

OK, I am back and have re read some stuff and considered how best to help. Here is the thing, in the Lucas formula he has threw trial and error been able to formulate an add back system that works for the 3 part schedule and to try the same add method with other products may just be counter productive. Over all when you use or study his formula, if you can do it according to how he says then it is less maintence then many other nutes and feeding schedules that do not correspond with MJ though many will disagree. Here is why IMO, he has it sorted out so that you can do the add backs in such a way that you may be able to go threw an entire grow with only 1 to 3 res changes depending on veg time really. If you do the first add back method, Just adding a topped off amount of PH'd water until you have topped off with equal amount of the res size, example you have a 23 gallon res you could topp off 23 gallon worth of times and just calculate needed PPM requirements and you could get about 3 weeks or more out of one res before a needed change, and then you could just do a change and flush for 12-12 then I would go with topping off with full strength nutes until the PPM arose above the acceptable level. There is the possibility of excess amounts of certain nutes being left in the water, but if you understand your strain you will quickly notice and this formula has been used so many times by so many growers that any little variables have not been enough to disqualify the formula from being the most popular out there.
Have more to say, but my attention span is wavering right now sorry.
Adieu

Yeah, mine does that alot. I ran a search on this forum and found some questions about it but not really anything that quite simply broke it down. Also ran one on Google but sort of ended up with the same drift--questions from others about it and answers I still don't get. If the 3 parts really are that much better would they be as effective if I just went by the chart on the back of the bottle?

PS Drippers still going hog wild with no cleaning!!

Many do just go off of the chart on the bottle. I will do some snooping around on different formulas and so on.
Adieu

Just for your bank of information guys I run an eighty gallon resi that has held solid for 2 full weeks now. When I do my full strength add backs I add the water first and then add in the required nutes. I am not trying to be exact on my ppms. I try to get within 100 ppm of my target range at finish.
I then check my ph and it has been right where it needs to be every time.(5.8-6.2) I have been really pleased with how it is reacting. I am figuring it is due to having such a large resi.

Thanks again Bear

Good luck to you hound -Jay

Mine holds about 25 gals total or something.....2 different reses...Bear I do want to try some different things like this 3 part but I know me well enough to know that if I don't understand it I will screw it up without a doubt. I have heard so many good things about the 3 part formula and feel better about trying something more complicated if it will increase yield etc....just afraid to jump into something I'm not understanding....I did study the back of the bottle and sort of went back and forth....yeah I understand this....wait....no I don't.....you get the idea. Any help, info, visual aids etc would be very appreciated. Thanks!

I will see what I can do. Have to get the little bear cub off to school and all that fun stuff.
Adieu