Can someone explain to me how to top up a reservoir (rez)? I just don't get it...

I haven't read all of the posts on this thread but here's my twopeneth. I had some great advice from "Dr. Who" a few months ago. I have followed this advice and tweaked it to my own setup and plants, so far this seems to be working fine. Everything looks healthy and happy.

I have 2 x 200 litre rez grows, each has a 200 litre top up tank gravity fed through a float valve (ballcock).

I fill my rez up with everything I want in there to 1.6 ec and 5.8 to 6.2 PH (if it is within this PH range I don't adjust it). I am 2.5 weeks into flower.
I then fill my 200 litre top up tanks with tap water (in my case it is zero - 0.2 ec straight from the faucet 7.2 PH), firstly I add cal.mag to 0.5 - 0.6 ec, I then add nutrients to just over 1/2 the rez strength (somewhere around 0.9 - 1.0 ec in my case @ 2.5 weeks into flower). If it is under 6.5 PH (in the storage tanks) I don't adjust it

As soon as the 200 litre storage tank has been used up or in 2 weeks time whichever comes first I do a rez change and do just the same again until I am in the last few weeks when I only add water and cal/mag to the storage tank (in other words as soon as the rez has used up its volume in added nutrient solution or in 2 weeks time I change out). I don't add any boosters or anything to my storage tanks just nutes, I do put additives into the main rez at every res change. When I res change I flush the system with clean water to remove the residual old nutrients and test the ec until it is 0.2 before I refill the rez.

I adjust the nute strength in the res itself. With this technique (in my setup) my rez strength seems to stay stable or drops slightly every few days.

I run top feed 60/40 coco/clay in 20 litre pots recirculated (24/7 recirculating pump water falling back into main res). My storage tanks are also recirculated 24/7 with a small pump from bottom of tank to top and water falling back just to keep them fresh. I DO NOT have any air stones anywhere.

This works well for my setup but if your roots are in the main rez water then it may be more complicated adding nutes directly to the main res you may be better off adjusting the storage tank which IMO would take to long to get into the system. I suppose you could add it to the main rez very slowly. The flushing of the system before a refill would also probably cause problems (this (and root rot) is why I will never put roots into a rez ever again, I know it works for some but for me RDWC roots in res was a nightmare for over a year)

This is just how I have started to do it and it works for me and my setup, not telling people how it should be done as I don't have the experience to advise anyone (only been growing around 3 years).

Aqua Man said:

Ok your full res is EC 1.2 the plants drink 10 gal and as such ideally that concentration is going to increase as the plants are drinking slight more water than taking up food so the EC increases as the plants drink... Say 1.3 now after they drink 10 gal. You add back a solution of 33% the EC drops back to 1.2 and you are pretty close to where ya wanna be.

Like at @Wastei it depends on the strain some feed more than others and I prefer 33% add back to achieve the starting ppm. After doing it a for a bit you will find a number that works best for your conditions and strains.

I suggest starting at 33% as a target. So if ya add back 33% and end up with the same EC observe the plants if all is good stick to that.

If EC after add back is lower than originally then you need to bump the overall ppm up. I suggest no more than 20% at a time so I may increase the res EC to 1.4 and add back 33% of 1.4 to dial it in

If the EC is higher than originally then you need to lower the overall ppm. I may drop to EC of 1.0 and add back 33% of that to dial it in.

Again it's a guideline and will take some practice but pays dividends in understanding you plants nutrient needs and all but eliminates nutrient issues.

It's just allows you to really understand the plants nutrient uptake and dial right in you feeding. If you have adequate nutrient ratios to start with you will eliminate any and all toxicity or deficiency issues by giving the plant exactly what it's asking for.

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Sorry I'm late to the party but i do have a question for you aqua;
You guys where referencing a 40 gallon res with 10 gallons missing for the 33% add back solution to work. Does this 33% math only work when 25% of the water in the res is missing? Say i have a 20 gallon res (my target ec is 1.2) and 2 gallons was uptaken by the plant overnight (the ec stayed the same at 1.2) Could i add 2 gallons of the 33% of the target ec (which would be 2 gallons at .4 ec) back and the math would still work?

so i made myself this chart to follow. Is this correct with your method?

RCJR said:

so i made myself this chart to follow. Is this correct with your method?

20 gallon RDWC res

20 gallon res change with fresh water and nutes to the desired EC range (1.2 EC at ph of 5.

Wait a day or 2 until the water level drops (ideally the EC should be 1.2 or 1.3 at this point)

Make a 33% solution (.4 EC) in separate container and add back until the res is full again (i don't have a way to see exactly how many gallons the res is low so ill make more than what i think it will take)

Once the res is topped off with this 33% solution and the EC is at the target range of 1.2 (at 5.. Your nutes are dialed in.

If the EC is higher than 1.2 (at 5. after the 33% top off your target EC needs to be lower

If the EC is lower than 1.2 (at 5. after the 33% top off your target EC needs to be higher

Don't increase or decrease more than 20%at a time

After you have filled the system with 20 gallons of top off solution it's time for a complete res change​

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i have no idea why the number 8 is an emoji? but the faces are supposed to be a number 8