Overflow and drains in Tom's tanks

Aug 18, 2010
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Hi Tom, I hope you can solve my questions.

As far as I know, CPR overflow drains don't run at full siphon, how do you deal with the air being injected down the pipes?
If air is sucked down the drains, the wet dry zone, if sealed, will end up filled with air.

Do you use valves in the drains?

I'm trying to reduce the velocity of the water down my drains, and I remember you saying that running 2 drains at low velocity degases less CO2 than having one of them running fast and the other slow.

Thank you.
Best regards.
 

Bala de Plata

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Sep 10, 2014
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I know my opinion will come wiry less weight, but I run a cpr 90 overflow with no modification at around 700gph and do not seal my sump. There is vet little noise to no noise and I can maintain approximately 65-70ppm of co2. I go thorough one 5# a month at $10 a fill.

This is relatively cheap as far as my time is concerned.
 

Tom Barr

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I use the larger CPR overflows, but the other types work well also, main things: keep them quiet, you generally do not need to push them at max flow rates, seal the filter below, use a CO2 reactor.

This helps overall issues with the CO2 delivery and maximizes the filtration.

An over sized dual pipe (or 3 like bean animal) overflow pre filter is very useful and then run it at 1/2 the rated capacity.
 
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ltb420

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You will have to modify the CPR to work in that way. Gerry has some excellent videos of his in action. I even borrowed his idea of using an elbow on the trickle tube to quiet it even further. Gate valves are more precise and will make it Easier to adjust the flow. Here are a couple of pic's so you get an idea.
epuzajy2.jpg
rybypeza.jpg
 
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Aug 18, 2010
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Thanks ltb420

I do understand the principle, but I'm almost sure that's not the way that Tom is running his overflows as I can see from some videos. Just curious about how he deals with that.
Can be very low flow rates from the return pump the key?

Regards.

- - - Updated - - -

Thanks ltb420

I do understand the principle, but I'm almost sure that's not the way that Tom is running his overflows as I can see from some videos. Just curious about how he deals with that.
Can be very low flow rates from the return pump the key?

Regards.
 

ltb420

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May 31, 2012
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You still need a decent amount of flow. All we have done is modify the overflow boxes to handle the extra flow without adding unnecessary turbulence. In the regular configuration you would just outgas more CO2. I believe reducing the turbulence in the overflow box is the key.
 

Tom Barr

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Flow rates can help, you should experiment with them.
Generally, less flow rates= less O2 and if you have a higher fish load, that can be an issue with low flow.
 
Aug 18, 2010
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I tought that lowering the flow would be a bad thing, but actually things got better in my tank after I changed the pump, perhaps I was overreacting with the flow, using a 90W pump on a 80 Gal tank. Things got better and for the last 3 months it's only using 25 W.

Perhaps I'm overreacting with the overflow itself too, I remember reading a post from Tom, regarding that his tanks degassed all CO2 in about an hour, doesn't happen to me. Actually it takes all night to increase PH by 0.8 units, never degasses all the CO2, neither faster. My Wet dry tower is sealed, but it ends up with gas build up during the day, and negative pressure during night. I think that water in Tom's drains trickles down the tube, allowing any gas build up to escape, because from what I see, that drains are not full siphon. Forgive me if I'm a bit intense with this matter, I just want to check my measurements are correct and Tom's tanks are perfect to compare, he's the "mythkiller".

I haven't seen any noticeable between having the wet-dry zone completly sealed and allowing a small area to let gas escape. To prevent any gas build up that causes backpressure in my overflow box, I inserted an air tubing to let the build up to escape, and measured PH via American Pinpoint Meter. The difference between those 2 scenarios was only a 0.07 PH drop aprox., higher in the airtight case of course. But affecting the water drop in the overflow caused a much significant difference. If this is correct, and if Tom doesn't have any build up in his wet-dry towers (He answered that before), any gas build up is escaping from his drains without causing too much trouble (Look at his tanks :D).

I tried a very different range of flow from the return pumps, but even with the lowest flow and having a reduced agitation in the wet dry zone, I still have that gas build up, that's why I decided to leave the tubing.

Regards

- - - Updated - - -

I tought that lowering the flow would be a bad thing, but actually things got better in my tank after I changed the pump, perhaps I was overreacting with the flow, using a 90W pump on a 80 Gal tank. Things got better and for the last 3 months it's only using 25 W.

Perhaps I'm overreacting with the overflow itself too, I remember reading a post from Tom, regarding that his tanks degassed all CO2 in about an hour, doesn't happen to me. Actually it takes all night to increase PH by 0.8 units, never degasses all the CO2, neither faster. My Wet dry tower is sealed, but it ends up with gas build up during the day, and negative pressure during night. I think that water in Tom's drains trickles down the tube, allowing any gas build up to escape, because from what I see, that drains are not full siphon. Forgive me if I'm a bit intense with this matter, I just want to check my measurements are correct and Tom's tanks are perfect to compare, he's the "mythkiller".

I haven't seen any noticeable between having the wet-dry zone completly sealed and allowing a small area to let gas escape. To prevent any gas build up that causes backpressure in my overflow box, I inserted an air tubing to let the build up to escape, and measured PH via American Pinpoint Meter. The difference between those 2 scenarios was only a 0.07 PH drop aprox., higher in the airtight case of course. But affecting the water drop in the overflow caused a much significant difference. If this is correct, and if Tom doesn't have any build up in his wet-dry towers (He answered that before), any gas build up is escaping from his drains without causing too much trouble (Look at his tanks :D).

I tried a very different range of flow from the return pumps, but even with the lowest flow and having a reduced agitation in the wet dry zone, I still have that gas build up, that's why I decided to leave the tubing.

Regards
 

Tom Barr

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Jan 23, 2005
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Well, folks can certainly have so little flow or current they have little degassing, there's a balance between them. With canister filters, it's much worse and more variation.
Wet/dry filters cure a lot of issues, but they cannot eliminate everything.

It's a balance of incoming CO2 and out going.
Same for O2.

Fast response: good O2 and rapid degassing of CO2 when you have the CO2 turned off at night.