LUCAS FORMULA (Part 2 - Addback Calculations) *from another site
The Lucas Formula: Addback
the markup formula uses the target tds, and a current tds, to calculate the percentage difference, then use that percentage to multiply against the 8ml that produces the target
so if for example the target is 1300 and the current is 900 with a 50 gallon res it maths out like this
target/current-1*8*Res Size=how many ml of nutes to add to the res
1300/900-1*8*50=178 total ml of nutes to add to the res
phew, you forced me to remember that, thanks
this formula is much more accurate than a 33% addback. It is based on markup math, and produces a nute dosage that will tend to be slightly too much, the TDS will be overshot
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
what counts is to get enough nutes added back to get up to the target TDS, of 1300-1400
the two formulas are predicting that to raise TDS 400 points will take between 125 to 172ml of nutes
once you do it once, it will be the same the next time... you just need to get into the ballpark, or raise TDS in steps..
> with the add back are you also adding water?
good question
the reservoir should be topped up with water before taking a TDS and pH reading
Only After the reservoir is full, should you take TDS and pH readings, and add nutes. With the 33% addback approach, you can nute the water before it is added to top up the res, but it wont guarantee that the TDS will get back to 1300, you may still need to add additional nutes..
for example, some light to res ratios require 100% nuteing of the addback water, in order to achieve 1300TDS the nute in the addback water approach, involves mixing nutes in the water that is going to be used to top up the reservoir. The benefit in DWC, is that you dont have to pump out, to dilute the nutes being added to the root zone.
Do not add pure undilited nutes to a DWC root zone, it will kill roots, and can cause entire plants to suddenly droop and die.
some warnings
in Ebb flow it is safe to add pure nutes to a res, but in DWC it is NOT safe to add pure undiluted nutess to the res that has roots in it
in order to nute a DWC container, it needs to be pumped out into a non root holding container, or at least several gallons worth.
Then the nutes get diluted in the pumped out water, before putting the nuted water back into the DWC root zone.
>The life of a rez on add back?
> what is your opinion of maintaining a setup, be it veg or bloom, at a target TDS for multiple crops without a rez change?
I believe it is possible to go 3 crop cycles on the same res, before pH becomes more difficult to manage, and an unreasonable amount of pH down is required to keep the res within the working pH range of 5.2-5.8 for a DWC type root zone, where they are always wet.
If the roots were in ebb flow, I would move the working pH range to 5.5 to 6.5, because when a pot of medium dries out in an intermittent irrigation system, nutes become concentrated, and pH drops in the root zone, to the same target as the constantly irrigated roots thrive at.
That is my best explanation to why there has always been a persistent belief that plants in soil or soilless medium, need a pH of 6.3 instead of a hydro pH of 5.3.. betewen irrigations the nutes concentrate and the pH drops
tangent, the bacteria that digest raw organic material, and turn it into water soluble nutes, like a pH above 7
back on track
How can we determine when a reservoir has passed its Useful Life? I think the length of time will depend on the size of the res.
For example, I think a 100 gal res for a 1k, will last longer than a 25 gallon res for a 1k.
so what are the parameters that will help us notice when our reservoir is "expired"
this assumes the res is kept full by an autotopping system, and that TDS is kept near original values, by adding nutes. This also assumes RO water. If you use tap, the buildup of calcium will require excess amounts of pH down, and the plants will get P overdose problems
1. The plants look like they are suffering, downcurl leaves, lack of lushness, lack of greenness, spotted leaves, lack of vigor, low yield, etc. Dump the res.
2. If there are no bad health symptoms, and yield does not drop, all else being equal, the res is not expired.
3. An aging res will get out of pH range, and require too much pH adjustment. Generally, with RO water, which adds no calcium, there will be a very slight pH increase over time, this is from unused P and K I think. Im under the impression the plant grabs all the N, which makes pH drop, and leaves a lot of the P and K in the res.. (someone help me out with the science, looking for + and - signs from the growing hydroponic tomatoes publication by Papadopolous.., the valence of the nutrient ions)
anyway, if a res becomes difficult to keep the pH down, dump it
beware a res that suddenly has very low pH, in the 4's. it can happen very fast if roots are rotting and dying. Do not use hydroguard to cure this, what is needed is more oxygen. A bubbler that works fine in the winter but has trouble in the summer, has too small an airpump.. use 1 watt of airpump per gallon of water, and you wont have temp problems until you get above 74F.. I digress, btw, ebb flow has no problem with 80F nutes..
background
plants dont really eat and excrete like organisms with digestive tracts. plants are the unique interface on earth, that captures and packages sunlight, for all the other Carbon Based Organisms that populate the globe
but when pH down interacts with alkaline substances like calcium, the two oppositely electrically charged ions bond and cancel out to a neutral salt, which forms a sediment.. I think its harmless, but, it looks bad, and can be syphoned out
I think the biggest issue with a single source nutrient though, is that there will be accumulations of nutrients of some types, that are underused, and build up in the res.
If anyone does any testing on res life, I would love more data... commercial greenhouses, Im told, dont dump their reservoirs, but they have nute dosers that can add N or P or K individually, and they can test for buildup of individual nutes
those are the parameters I think that need to be monitored, with pH being the canary in the mineshaft.. and where Yield is the final criteria
> (Advanced-Nutrients)
Those are very high quality nutes, use them the same as you would GH Flora series.. and note that you CAN use standard GH nutes recipes, that is 15g-10m-5b for veg, and 5g-10m-15b for bloom, where g is grow, m is micro, b is bloom, and 15 means milliliters per gallon..
there are reasons to believe that the "Lucas Formula", which was pH's idea, not mine, lacks nitrogen in veg, and that even extra nitrogen in bloom can be very productive..
there is no one nutrient that has the magic.. the magic is in the veg time, and CO2 delivery (airflow)
> That would be a profound discovery to me if it's true that FloraGro leaves the res sitting at the ideal ph
, there is no magic bullet, but, if you are finding that Grow makes your pH more stable, just do it!
fwiw, what makes Grow different is that it has a different Nitrogen profile..
that is, Micro is 5% Nitrogen, of which 4.7% is Nitrate, and .3% is Ammoniacal, whereas Grow is 2% nitrogen, of which 1.75% is Nitrate, and .25% is Ammoniacal.
Ammoniacal nutes tend to drive pH in the opposite direction of Nitrate nutes..
in any case, Ive come to the general conclusion that more nitrogen than 0-8-16 provides is not a bad thing.. You can do well by just following stock GH directions, if you already own the Grow bottle..
Let me put it this way.. with 0-8-16, Ive yielded .57 grams per watt in 50 days. Using Flora Nova Grow to veg (same as 15-10-5 in flora series), not changing the res, and doing all addbacks with Flora Nova Bloom (same as 0-8-16) I got my best yield ever, .79 grams per watt, in 50 days.
I think more nitrogen than 0-8-16, especially in veg, makes the buds fatter. The stems were much bigger in diameter too.. and the leaves were bigger and greener..
