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Old 03/26/2020, 09:46 AM   #1
Yuki
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Join Date: Oct 2006
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Crazy RODI Creep issue

So, I've been having a problem with algae in this 300 gallon I take care of. Every parameter comes out perfect. Zeros. I believe I have found the issue but don't know why. The TDS goes spikes up to 1000tds after the membrane. It relatively quick starts to go down and then get to 7tds. But, it takes approximately 15-20 minutes for the TDS to getr down to 0 after the DI. This is a real problem since I am doing direct top off. So, I think I'm constantly topping off with terrible water. I have another 300 gallon that I take care of and It has direct top off from RODI and it stays at 0. I don't get it. I thought it was Chlomines eating up the membrane and DI so I put a stage of catalitic carbon. That didn't help. I checked the TDS coming from the source and it is 245. Which is pretty normal. SO, how am I getting this TDS creep and How do I fix it? Please help. This one is beyond me.


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Old 03/26/2020, 11:10 AM   #2
Opus123
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Quote:
Originally Posted by Yuki View Post
So, I've been having a problem with algae in this 300 gallon I take care of. Every parameter comes out perfect. Zeros. I believe I have found the issue but don't know why. The TDS goes spikes up to 1000tds after the membrane. It relatively quick starts to go down and then get to 7tds. But, it takes approximately 15-20 minutes for the TDS to getr down to 0 after the DI. This is a real problem since I am doing direct top off. So, I think I'm constantly topping off with terrible water. I have another 300 gallon that I take care of and It has direct top off from RODI and it stays at 0. I don't get it. I thought it was Chlomines eating up the membrane and DI so I put a stage of catalitic carbon. That didn't help. I checked the TDS coming from the source and it is 245. Which is pretty normal. SO, how am I getting this TDS creep and How do I fix it? Please help. This one is beyond me.
Not really sure. Just a FYI on chloramines. They will not hurt the RO membrane but it will use up the DI. Chlorine is what will kill the membrane.

Your rejected water isn't going to be any where near 1000 tds so I'm not sure how you can get such a high number for the tds creep. Have you tried a new RO housing?


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Old 03/26/2020, 03:00 PM   #3
Yuki
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The TDS meter is inline before and after the DI and it higher going into the DI than it is coming out eventually after it get rid of the mixed high TDS water. So, i know the creep is happening in the membrane housing.


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Old 03/26/2020, 03:02 PM   #4
LQT
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If you’re hooking up your RODI direct to a float valve to top off your tank, I would caution you... if that ATO float ever gets stuck in the open position, you may be looking at a serious flood hazard.

In addition, having the RODI unit constantly cycling on and off will cause you to deplete your DI resin at a much faster rate due to the TDS creep as you’re experiencing. Make larger volumes of water in batches and use a DI bypass valve to flush out TDS creep water upon system start up.

TDS creep occurs because when a system is shut down, you have dirty, high TDS water on the waste water side of the membrane and very low TDS water on the permeate (product water) side of the membrane. As a unit sits idle, the low TDS product water on the permeate side of the membrane will aggressively seek to reach equilibrium with the dirty waste water side of the membrane. So as it sits, TDS is drawn from the dirty side of the membrane, through osmosis, until it reaches equilibrium with the clean permeate side of the membrane.

Enter the DI bypass valve, which is a 3 way valve between your RO membrane and your DI stage. Upon startup of a system, you use the DI bypass valve to flush out the TDS creep water that has accumulated on the permeate side of the RO membrane, diverting it away from your DI resin and down the drain. This drastically improves DI resin life by not allowing this high TDS creep water to go through your resin. Upon startup, I usually let the bypass run for a minute or two. I make sure to position my TDS sensor between the membrane and the bypass valve so I can see the permeate side go from a high TDS creep number to it normal RO product water number (in my case, it’s 1). After all the TDS creep water has been diverted out of the system, only then will I allow the low TDS RO water go through my DI resin.

This is really why you should get away from directly connecting your RIDI unit to top off your tank. Use an ATO system like a Tunze 3155 or Spectrapure ULPC-ATO and store you’re top off water in an ATO reservoir. Manually top up your reservoir as needed.


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Old 03/27/2020, 12:18 AM   #5
Yuki
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Thank you. Good information. I think Iím going to have to make a reservoir one one system and maybe buy an emergency cut off leak sensor for the other. Itís just strange the difference between the two tanks.


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Old 04/24/2020, 02:42 PM   #6
joetomberlin
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Fully automated top-off with no TDS creep

I agree with LQT about using a reservoir and a system like the Tunzi 3155. However, I configure mine a bit different. The standard config has the Tunzi pulling water out of the reservoir and is the primary top-off controller leaving you to still manually make the makeup water and haul it to the reservoir.

First, I use the APEX ATK instead, sort-of. Instead of the two optical switches controlling the top-off water into the sump, they control the re-filling of a 10 gallon reservoir. The switches are set at ~ 1 gal level to turn on, and the full, or 10 gal lever to turn off. Feed water comes into the reservoir through a float switch as a backup shutoff. Instead of the ATK powering a pump, it opens a solenoid valve on my 100 gal/day RODI to fill the reservoir. Since it takes about 2 hours to get the 8-9 gallons of water from the RODI, the initial high TDS for a minute or two becomes insignificant and no DI bypass is needed. I also use a permeate pump to reduce wastewater and it has no problem pushing the water through 30 ft of 1/4 in line with a 6 ft lift.

I then use a standard "Double" float setup from topoff.com with an aqualifter AW-20 pump to top-off the sump from the reservoir. I could add a float valve to this feed as another backup in case the top-off switch floats sticks, but I'm not sure the low pressure of the AW-20 can push open the valve. Instead, I put an additional optical switch in the sump (above the water level when the main pump is off) and it connects to an extra port on the ATK. My main APEX controller monitors this switch to turn off the top-off floats & pump in case they stick and try to overfill the sump. The ATK still has a 4th port which get a leak detection probe for the bottom of the cabinet in case any systems fail and it will shut off everything except the lights.

Pros: Fully automated top-off system, no TDS creep, multiple safeties
Cons: More expensive and to get full benefit, need an APEX controller

On my 115 gal reef tank, the reservoir gets refilled about every 5 days. The RODI does not just sit idle though, as I feed a pressure tank, through a check valve, that goes to an icemaker and an RO faucet. This is where my DI resin will get it's most use. Although, since the icemaker doesn't care about TDS, I could pull it's water off before the DI.


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Old 04/25/2020, 04:23 PM   #7
Opus123
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Quote:
Originally Posted by joetomberlin View Post
I agree with LQT about using a reservoir and a system like the Tunzi 3155. However, I configure mine a bit different. The standard config has the Tunzi pulling water out of the reservoir and is the primary top-off controller leaving you to still manually make the makeup water and haul it to the reservoir.

First, I use the APEX ATK instead, sort-of. Instead of the two optical switches controlling the top-off water into the sump, they control the re-filling of a 10 gallon reservoir. The switches are set at ~ 1 gal level to turn on, and the full, or 10 gal lever to turn off. Feed water comes into the reservoir through a float switch as a backup shutoff. Instead of the ATK powering a pump, it opens a solenoid valve on my 100 gal/day RODI to fill the reservoir. Since it takes about 2 hours to get the 8-9 gallons of water from the RODI, the initial high TDS for a minute or two becomes insignificant and no DI bypass is needed. I also use a permeate pump to reduce wastewater and it has no problem pushing the water through 30 ft of 1/4 in line with a 6 ft lift.

I then use a standard "Double" float setup from topoff.com with an aqualifter AW-20 pump to top-off the sump from the reservoir. I could add a float valve to this feed as another backup in case the top-off switch floats sticks, but I'm not sure the low pressure of the AW-20 can push open the valve. Instead, I put an additional optical switch in the sump (above the water level when the main pump is off) and it connects to an extra port on the ATK. My main APEX controller monitors this switch to turn off the top-off floats & pump in case they stick and try to overfill the sump. The ATK still has a 4th port which get a leak detection probe for the bottom of the cabinet in case any systems fail and it will shut off everything except the lights.

Pros: Fully automated top-off system, no TDS creep, multiple safeties
Cons: More expensive and to get full benefit, need an APEX controller

On my 115 gal reef tank, the reservoir gets refilled about every 5 days. The RODI does not just sit idle though, as I feed a pressure tank, through a check valve, that goes to an icemaker and an RO faucet. This is where my DI resin will get it's most use. Although, since the icemaker doesn't care about TDS, I could pull it's water off before the DI.
You probably should tee off before the DI for any drinking water. That is what most recommend since DI is not foot grade quality.


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