i hear of people saying to shoot for a ppm range of 1350 at .7 conversion my meter does .5 so do i shoot for 964? im using pbpgrow for veg and pbpbloom for flowering, somewhere i heard 15ml/gal and 5 ml/gal of calmag plus gets me the same(there abouts) as the lucas formula. is this correct? is this equation right for add back? target current target ml rez 964 - 0 = 964 / 964=1 x 15 =15 x16=240ml of bloom needed to reach 964 ppms? what about my calmag plus ?it will be added too but dont know how to figure it into the equation?
How long have you been using the Lucas formula? If the answer is: This is my first time. Then dont worry about 'add backs'. Just dump the rez every 10 days and refill with fresh. Focus on add back calculations once you have the experience to know when the numbers need to be ignored and the plant must be 'read'.
There are NO ADDITIVES used when following the Lucas Formula. All it does is screw up the stability of the mix and cause additional pH chasing. I'll probably be saying this for another 5 years until people catch on but here goes...... YOU DON'T NEED TO ADD CAL/MAG TO RO WATER WHEN USING THE LUCAS FORMULA. Thank you. I'll be here all night folks. If you're getting what LOOKS like a deficiency with the Lucas Formula and RO water(Usually around day 30), adjust your pH to around 6.0 to 6.1 for a week or so and your girls will look spectacular. Let it drop back down to around 5.5-5.8 after that for the remainder of the grow. As for the add-back, I'm still running the simple dump and re-fill. It's so cheap and all I do is add RO water so my maintenance is dead simple. Since switching to 8ml/gal of FloraNOVA bloom with RO I spend almost no time at all on the res and all the rest of what little time I DO have on my plants. I mix the solution, pH appropriately and then walk away. I never adjust the pH from that point on, only add RO. It's just too simple. I'm also interested in the answer to your solution (without the cal/mag) for future reference. Thanks for bringing up the .5 and .7 difference
Hydroganic- do you have the spreedsheet table for the lucas formula. The link to it in the "ask lucas" thread is dead.
The link isn't dead, you just have to right click and "Save Target As..." http://www.angelfire.com/cantina/fourtwenty/articles/premixppm3b.zip Also if using PBP with RO water, you may need to add Cal Mag depending on the strain. For those of you unfamiliar with Lucas and interested in simple hydroponics I suggest reading this thread: https://www.cannabis-world.org/cw/showthread.php?t=892 And respectfully Klutter, when topping off with pure water, rather than dumping a reservoir after a given number of days I would suggest dumping when you have added back 100% of your reservoir. IOW if you have a 40 gallon res, once you have added back a total of 40 gallons of RO water then dump and refill. Alternately, you can add nutes to the reservoir in addback water with the goal being to bring the nutes back to 1300-1400 @ 0.7 conversion. With this strategy, a single reservoir change at harvest should be sufficient. Many people(myself included) go 2-3 harvests between complete reservoir changes. I top up every day or two with pure water and adjust nutrient strength once a week. This is the most efficient use of your nutrients as you are only wasting them(dumping them down a drain) once every 4-6 months. I know that opens up the argument about flushing your plants during ripening, but I just let my ppm drop down to 800-1000 (@ 0.7) the last week or two and get the same quality(in side by side tests) as a 7-10 day flush.
Another reason I recommend skipping the flush is the fact that starving your plants at the end of their life cycle is the opposite of what you should be doing. You should be trying to fatten them up. Flushing is needed in soil with nutrient accumulation, makes no sense in hydro.
how would i do the addback using pbp and calmag would the veg formula be the same ratio(15ml/grow 5ml/calmag)?
If Lucas has worked it out, you'll find it in this thread HERE.... I prefer things straight from the source
From the thread: "the inverse formula, using markdown math, produces a more conservative estimate it goes like this 1-(current/target)*8*res size=total ml of nutes to add to res" This was using FNB at 8ml/gal as an example to get to the starting/target tds. You would change that number to 20 (15 ml PBP and 5 ml Cal-Mag). So your formula would be: 1-(current/target)*20*res size=total ml of combined nutes to add(this incl. Cal-Mag) Your res looks like 16 gallons from above post? So: 1-(current/target)*20*16=(3/4) PBP and (1/4) Cal-Mag Example. TDS when 15 ml PBP and 5 ml Cal-Mag added to your water is 1000. You check your res after topping off with pure water and it is 800. So: 1-(800/1000)*20*16=64ml needed. Thats 48ml PBP and 16ml Cal-Mag.
what does the 1- do? is it like this? current target ml res 700 / 1000 * 20 * 16=300*20=96ml=72ml bloom +24ml cal mag does this seem right? nevermind its for smaller numbers hey ocd thankyou
if im right its easier for me to do it this way? current divided by target than -1 than mutiply by 20ml than by 16gals=total ppm than minus 75% or 25% to get bloom and calmag ratios. is this correct?
1-(current/target) gives you the percentage your current TDS is lower than your target yes it is 1-(current/target) * ml/gallon * res size in gallons Those number are right (current/target)-1 will be a negative number, but yes, that is the pecentage that your current tds is lacking. This formula will give you the correct amount, only as a negative.