How often do I need to change the water in my reservoir?

[Fecal_Feaster]

I have an ebb and flow system with a 55 gallon reservoir, I plan to use RO water with drip clean and a couple airstone along with my nutrients. I've been told you have change the water every 1-2 weeks or you'll get algae and salt build up but if I'm using airstones and drip clean is that really necessary or can I just keep topping off the fluids as they deplete?

 

[Hydro Hippie]

I have an ebb and flow system with a 55 gallon reservoir, I plan to use RO water with drip clean and a couple airstone along with my nutrients. I've been told you have change the water every 1-2 weeks or you'll get algae and salt build up but if I'm using airstones and drip clean is that really necessary or can I just keep topping off the fluids as they deplete?

I do a week to 10 days on a resivoir change. 10 days in the beginning of the grow and maybe even every 6 days at the end. Just depends how fast they are eating.

As long as you are running a clean resivoir (no beneficial microbes) good aeration, algi prevention and a chiller you could get by with 2 weeks. The only problem with going longer between changes is your ppm start to go down so you will need to add nutrients. The only problem is you kinda have to guess what nutrients have been used up and what's left. If your a beginner this could be difficult.

 

[White.Black]

Water change every 2 weeks work for me. Adding (topping up) nutes every 3 days, some local GH clone.
Quarter of recommended dose to a Dwc 10 gallon. I'm adding about 3 to 4 gallons.

Water at 18c, adding small amounts of hydroguard.

No root rot, algae or any kind of root problems.
Every week is safer obviously for nute lockout, but in my case every 2 works just fine.

I read everywhere it's recommended a week, and I did my first grow like that, but now I found out that it works every 2 weeks so less waste / hassle.

 

[neckpod]

Depends on a lot of factors really, i dont really change it out in veg as its simply not needed but during flower it will be every 1 to 2 weeks max. it depends on how big your system is too i run 6 x 62ltr totes with a 150ltr control tote. probably got 40ltr in each location and 110 in the control. the bigger the system the more stable it will be and potencially needs less change outs..

 

[rkymtnman]

can I just keep topping off the fluids as they deplete?

are you topping off with water or with nutes added?

 

[Redlig]

Awe man im going to look sooooo lazy...my tanks are 40ish gallons and ill run 14 roughly 24in plants and instead of changing it they drink and eat so much i just top it off. I change it once when i flip other than that i top off with new water/nutes till chop then ill run fresh water for a week. However i dont over feed and my tanks are aerated and kept pretty cold. Only thing i really focus on is ec and ph. If it gets out of wack or I see signs of deficiencies then i may change it out other than that i let er ride

 

[Delps8]

This paper by Dr Bruce Bugbee might be of interest.

 

[Redlig]

This paper by Dr Bruce Bugbee might be of interest.

Wow ok so that was a cool read and made me think of something...so when i change my tanks i use the old water to water my mothers. I started paying attention to it and i bet there is still good stuff in there because they can look a little rough/ yellowing(old soil) and ill water them with that and they come right back.

 

[Chow13]

What I read when I started with a RDWC is that you want to change your water once you have "Topped" up the same amount as what is in the system.
The only time I do not follow that rule is when I am first starting a grow. Plant does not drink enough and I am not a fan of adding unmixed nutrients to the existing mixture.

 

[Fecal_Feaster]

are you topping off with water or with nutes added?

With nutes, the reservoir is also outside the light/heat of my grow tent and in front of a window ac unit to help with algae prevention

 

[Fecal_Feaster]

This paper by Dr Bruce Bugbee might be of interest.

This is probably the most informative article I've read on the subject, thanks

 

[Fecal_Feaster]

Awe man im going to look sooooo lazy...my tanks are 40ish gallons and ill run 14 roughly 24in plants and instead of changing it they drink and eat so much i just top it off. I change it once when i flip other than that i top off with new water/nutes till chop then ill run fresh water for a week. However i dont over feed and my tanks are aerated and kept pretty cold. Only thing i really focus on is ec and ph. If it gets out of wack or I see signs of deficiencies then i may change it out other than that i let er ride

This is probably what I'll do during veg and dump/refill the reservior every 2ish weeks during flower. The suggestions of doing weekly doesn't seem economical with a reservoir this big

 

[Delps8]

This is probably the most informative article I've read on the subject, thanks

You're welcome.

But, wait, there's more!

It took me a bit to find this. The guidance at the bottom of the page sums it up nicely.

 

[rkymtnman]

With nutes, the reservoir is also outside the light/heat of my grow tent and in front of a window ac unit to help with algae prevention

the thing you have to consider is your nute profile will change as you keep adding more nutes and the plants use them up. you might end up with too much or not enough of each nute

 

[Delps8]

the thing you have to consider is your nute profile will change as you keep adding more nutes and the plants use them up. you might end up with too much or not enough of each nute

That's the whole issue in a nutshell - different chemicals in the nutes are taken up at different rates so adding RO/water dilutes the mixture but maintains ratios whereas adding nutes, even diluted 4:1 as Bugbee does, will replenish the rapidly depleted chemicals but will tend to build up the amounts of the chemicals that are taken up slowly. Eventually, that imbalance will cause nutrient deficiency or nutrient toxicity.

Conventional wisdom seems to be split on between topping off with water only vs topping off with nutes and, being somewhat (cough, cough) of a helicopter plant daddy my take was to have things at "optimum" levels so I was adding back nutes to get to the previous level of TDS. The road to hell is paved with best intentions and, in this case, what seemed optimal to me was not optimal to the plants.

When I read the Bugbee research, I built a little "model", as shown below. I'm sure it's quite inaccurate* but it helped me understand that even if the TDS of the res drops "a lot", there's still plenty of nutes to keep the plants at the "sufficient" nutrient level.







The big win for me was that comments at the bottom of the CannaStats page. My res holds 28 gallons of nutes and it's in a 2' x 4' tent so I'm right in the ballpark of 3 gallons per square foot. And, per the graphic, I did have a drop of ≈ 25% in the res. Adding back just RO works fine for me and swapping the res at about 25% down or every 2 weeks is a big labor saver for me (two plants in a res that holds 28 gallons of nutes).

*I realize that it deals with elemental PPM not TDS in the res but I did help illustrate what types of changes were going on in the res. I'd love to see actual data but the cost/benefit isn't there for me.

 

[Delps8]

A short video from the Jack's website.

 

[rkymtnman]

That's the whole issue in a nutshell - different chemicals in the nutes are taken up at different rates so adding RO/water dilutes the mixture but maintains ratios whereas adding nutes, even diluted 4:1 as Bugbee does, will replenish the rapidly depleted chemicals but will tend to build up the amounts of the chemicals that are taken up slowly. Eventually, that imbalance will cause nutrient deficiency or nutrient toxicity.

Conventional wisdom seems to be split on between topping off with water only vs topping off with nutes and, being somewhat (cough, cough) of a helicopter plant daddy my take was to have things at "optimum" levels so I was adding back nutes to get to the previous level of TDS. The road to hell is paved with best intentions and, in this case, what seemed optimal to me was not optimal to the plants.

When I read the Bugbee research, I built a little "model", as shown below. I'm sure it's quite inaccurate* but it helped me understand that even if the TDS of the res drops "a lot", there's still plenty of nutes to keep the plants at the "sufficient" nutrient level.

View attachment 5217918


View attachment 5217919


The big win for me was that comments at the bottom of the CannaStats page. My res holds 28 gallons of nutes and it's in a 2' x 4' tent so I'm right in the ballpark of 3 gallons per square foot. And, per the graphic, I did have a drop of ≈ 25% in the res. Adding back just RO works fine for me and swapping the res at about 25% down or every 2 weeks is a big labor saver for me (two plants in a res that holds 28 gallons of nutes).

*I realize that it deals with elemental PPM not TDS in the res but I did help illustrate what types of changes were going on in the res. I'd love to see actual data but the cost/benefit isn't there for me.

now that i've switched over to drain to waste, all those issues went bye-bye.

 

[futurebanjo]

very interesting stuff, thanks for the info all.

I'm just gonna go with not refreshing the rez until I flip to 12/12, and flip to bloom nutes as long as I can keep PH and EC under control/in range during Veg. I am using silver bullet though, in a very small preventative dose to hopefully stave off root issues, and my tank is quite large at 120L.

 

[farmerfischer]

Every two weeks is what i did with mine, but i had 25 gallons .. there is many things you can use to prolong changings now..

 

[rkymtnman]

Every two weeks is what i did with mine, but i had 25 gallons .. there is many things you can use to prolong changings now..

i use a 30 gal trashcan as my res. i made marks up the side at 5 gal increments to get a better idea of how much i was using in a week.