Why change water in hydro system?

Why PH do what it do

There was a thread a while back about the 33% add back rule.Meaning if your target ppm was 1000 you add back 333, When youve added back the total volume of your system you flush and replace.

This brings up flushing,Myself I run tap water via garden hose into the last pail ,pumping out from the res removing all the nutes,I also lightly spray ea root ball/top feed ish.Once finished i fill the system letting it run for 24 hrs check with ppm meter,drain,refill with nutes.

I do this ea res change

Did a fair amount of reading about rdwc on here and other sites before getting started and throughout the first grow, I was asking the same question about not changing out the solution and saw others who run the same solution start to finish successfully. Some changed out at the flip. I figured it was worth a shot to see if I could simplify that part of the process and still have a good yield. I chose to do partial change-outs to help maintain a balanced solution and not become over-concentrated in any area. Will see in a couple weeks how it turns out at the end .

The system is setup to automatically drain ~30-50% per week and it refills and doses current culture nutrients whenever the water level drops to match predefined EC targets following their schedule. Things have gone really smooth (albeit their schedule had the EC a bit high for week 6 for me) and I think it's reduced the water consumption overall. System volume is 55 gallons and the top off manager has filled 385 gallons over the last 11 weeks and that includes all the transpiration that's happened. Last run I probably used ~800 gallons doing full change-outs every week (and a lot more nutrients I would wager).

RDWC user

I change the reservoir when I feel like it. Its not a hard and fast rule for me.

Generally will change once or twice in veg depending how long im vegging for and 2 times in flower. Once 2 weeks in and once at week 6 to change to my finish recipe.

I run large 120gal systems for only 8 plants so I find I need to do a full change out less. When I was running 5 gal buckets that hold 3.5gal of water I would be doing change outs every 2 weeks strict. Sometimes less. Once my pH starts dropping and im not in late flower its time.

My reasoning is that the plant will leave behind nutrients it doesnt need and those will build up over time.

Say your recipe is 10 dimes, 5 quarters and 3 nickels. You keep topping up with that same recipe. Only the plant is taking in 8 dimes, 4 quarters and 2 nickels between top offs. You are going to get a build up of the leftovers.

Certain nutrients compete with others for absorption. Particularly potassium, calcium and magnesium. But look up a Mulder's Chart to learn more about synergistic and protagonistic relationships between the various nutrients.

firsttimeARE said:

RDWC user

I change the reservoir when I feel like it. Its not a hard and fast rule for me.

Generally will change once or twice in veg depending how long im vegging for and 2 times in flower. Once 2 weeks in and once at week 6 to change to my finish recipe.

I run large 120gal systems for only 8 plants so I find I need to do a full change out less. When I was running 5 gal buckets that hold 3.5gal of water I would be doing change outs every 2 weeks strict. Sometimes less. Once my pH starts dropping and im not in late flower its time.

My reasoning is that the plant will leave behind nutrients it doesnt need and those will build up over time.

Say your recipe is 10 dimes, 5 quarters and 3 nickels. You keep topping up with that same recipe. Only the plant is taking in 8 dimes, 4 quarters and 2 nickels between top offs. You are going to get a build up of the leftovers.

Certain nutrients compete with others for absorption. Particularly potassium, calcium and magnesium. But look up a Mulder's Chart to learn more about synergistic and protagonistic relationships between the various nutrients.

Click to expand...

the article i posted from bugbee in 04 gives u as good of a referencers for the dimes quaters and nickles... thing about my breakdown of the article is the ratio of nutrients bein taken out of the plants is relatively a similar from an everything perspective besides calcium witch drops a lot towards the end.
basically a 20-5-20ish is being taken out the whole time based on my reading of the article... you would think hypothetically different growth stages w different morphologies would cause vastly different nutrients uptake... but based on the ratios from table 3 from the paper and my subjective thoughts about what happening (to the roots. fruits, flwoers, stems) durring those different stages... the ratios still tyurn out very similar.

hhere is another thing i found from ed rosenthal on recycling hydroponics.... he states a 3-1-3 will be sufficient for replenishment mix.. actually he calls for a 14-4-14... i thought it was rather close to the kinda 4-1-4 i drew from bugbee paper in 04

US9527778.pdf

id be curios if anyone can find a paper that debunks this stuff... or just a contrarian paper to check out would be cool

TintEastwood said:

Light reading.

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Click to expand...

good stuff.... the guy actually cites the bugbee paper from 04 that i been wortking off of to make these mixes. were bioth working off the same source material.... in bugbees paper he goes a little deeper into how to figure ur replenishment solutions based on the rate of growth of 4 things roots fruits stems and flowers... its gets a little subjective after that

i should say that some of the figuring i was doing at the beingin of the thread was wrong i think.... im not sure holding a 1.2 the whoile time is the correct way to go here... infact the more i read the article im thinking the cycling solution is going to extremely low nutrient... the replenishment ratios i posted above i would still hold to... but i need to rethink the concentration of the cycling solution and i think its going to be much lower than what i thought originally.

2 things from the paper....

Potassium (K). The supply of K is more constant with a lower level in the starter solution and a more concentrated refill solution

The plant tissue concentrations of all elements were ample in this study, and, in fact, K and P concentrations were excessive. After this study, we reduced the concentration of K and P in the refill solution to the level indicated in Table 4. The starting K concentration was 4 mM in this study, but our current starting K concentration is 1.5 mM, which is maintained at about 0.5 mM K in the circulating solution by adding 4.5 mM K in the refill solution.

if we break this down to ppm in terms of ratio what i think hes saying is hed be starting at 150ppm K.... after absorption the solution will be cycling 50ppm K.... each day theres a refill solution of 450ppm K.... witch should deplete back to 50ppm K very quickly.... repeat the cycle daily or whatever

this leads be to believe the cycling solution is going to be kept at a very low ec... but im working on that now if anyones got any thoughts

firsttimeARE said:

RDWC user

I change the reservoir when I feel like it. Its not a hard and fast rule for me.

Generally will change once or twice in veg depending how long im vegging for and 2 times in flower. Once 2 weeks in and once at week 6 to change to my finish recipe.

I run large 120gal systems for only 8 plants so I find I need to do a full change out less. When I was running 5 gal buckets that hold 3.5gal of water I would be doing change outs every 2 weeks strict. Sometimes less. Once my pH starts dropping and im not in late flower its time.

My reasoning is that the plant will leave behind nutrients it doesnt need and those will build up over time.

Say your recipe is 10 dimes, 5 quarters and 3 nickels. You keep topping up with that same recipe. Only the plant is taking in 8 dimes, 4 quarters and 2 nickels between top offs. You are going to get a build up of the leftovers.

Certain nutrients compete with others for absorption. Particularly potassium, calcium and magnesium. But look up a Mulder's Chart to learn more about synergistic and protagonistic relationships between the various nutrients.

Click to expand...

i would assume the PH drop is the alkalinity thge RO water right? or the non alkalinity i should say... what ur describing seems logical w RO filtered water as nuitrient diminish the buffer is almost non existant. if u were to replenish the nuitrent w the correct ratio and more importantly i think the correct form of acid you would be back to where u were... and by that i mean i think u would have to use nitric acid... if u use phosporic acid ur going to be right back where u are... once the phosporus is taken out the ph goes crazy... and u cant put enough phosporus in to keep the ph where u want it without the plants taking up excessive amount of the phosporus int he process... id look into making replenishment solutions w nitric acid.. thats my gameplan anyway

my thoughts on nuitrent competition is its only a problem if ur excessive w anything or ur ph is off... neither should be a problem if i thought i make a mistake in judge,ment or whatever id just dump and start over.. theres actually a rather large scope before nuitrents can get excessive.. even deep into the luxury stage ur not going to suffer any problems... its just a waste