Reef nutrition

RODI Replacement Cannisters

Question...my first stage of my RODI unit is very discolored and that tends to indicate it's time to replace it. My pressure has declined only by 1-2 PSI. Do i only need to replace the first canister or all three?
 

ofzakaria

Supporting Member
How many stages you have?
What's your first stage?
I change the first 3 stages once it reads anything not zero.

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ofzakaria

Supporting Member
Oh got it.
Well if it's me I would change all stages cause once you started seeing tds it might mean the di reain is depleted as well.
Otherwise start changing the first stages and keep do resin bit longer and see. But honestly I think it's not big diffrent cost wise so I would change all and start fresh.

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sfsuphysics

BOD
Staff member
First three stages are typical going to be a mixture of carbon and sediment filters, and often you'll have 2 of one kind and 1 of the other, a very common setup is a sediment filter then 2 carbon blocks, 2 just as a back up to make sure all chloramines are pulled out. The problem is carbon really doesn't have any color indicators to let you know that it's ready to change, any color that's on them is due to sediment that gets through that filter and really isn't what those filters are removing. Having some sort of flow meter that records how much water goes through them is the most ideal situation, however an easy second step is to have a tee with a valve right after the first 3 filters and periodically test the output with chlorine test strips, and the easiest way is to see how fast your DI resin gets used up, if you notice a very rapid change then it's pulling out more stuff than it was likely chloramines.
 

MolaMola

Supporting Member
Oooh - didn't know I could use chlorine test strips at that point to test for chloramine - will get some strips!
Jumping in with a related question - if you test your TDS at that T after the sediment and 2 carbons, could it be higher than the input TDS from the tap? Why would that be?
 

sfsuphysics

BOD
Staff member
Oooh - didn't know I could use chlorine test strips at that point to test for chloramine - will get some strips!
Jumping in with a related question - if you test your TDS at that T after the sediment and 2 carbons, could it be higher than the input TDS from the tap? Why would that be?
My chemistry is almost non-existent, but I believe you want "total chlorine" as opposed to "free chlorine" which I'm not sure detects chloramines.
 

RandyC

Supporting Member
My chemistry is almost non-existent, but I believe you want "total chlorine" as opposed to "free chlorine" which I'm not sure detects chloramines.
Correct. Free chlorine just tests for chlorine that is not bound to anything. You will need a test stripe that tests for total chlorine to detect chloramines.
 

ofzakaria

Supporting Member
My water source have chloramine which is the worst. That's why I use 7 stages rodi. It's an overkill but it last me more compared to when I ran 5 and 6 stages...
Also I try to keep zero tds water and change filters once last stage start showing 1 tds..

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Coral reefer

BOD
Staff member
@Jeff Rehling visual discoloration does not indicate time to change. It will look dirty quickly but work well for some time still. 1-2 psi drop isn’t much.
Your chloramine block probably needs to be changed every 1500 gal of total water through out depending on what one you use. That counts waste and product. Only way to know for sure is to monitor the galllns you put through it.
Text r call me if you have questions. Don’t have time or feel like typing a long response right now.
 

ofzakaria

Supporting Member
Oooh - didn't know I could use chlorine test strips at that point to test for chloramine - will get some strips!
Jumping in with a related question - if you test your TDS at that T after the sediment and 2 carbons, could it be higher than the input TDS from the tap? Why would that be?
I test Tds main input, at output of of carbon blocks(input of ro membrane) at input of di and at output of di.
My main input is aweful around 135,
My ro membrane output.is around 12 and my di output is 0

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ofzakaria

Supporting Member
@Jeff Rehling visual discoloration does not indicate time to change. It will look dirty quickly but work well for some time still. 1-2 psi drop isn’t much.
Text r call me if you have questions. Don’t have time or feel like typing a long response right now.
The only visual discoloration that indicate time to change is the color changing di resin. If you use color changing di resin, color is good indication to depleted.
That being said, it's all about tds for me, tds above zero, time to change

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