CalRx Aeration Tower / CO2 Removal from Effluent Project

[Dennis Cartier]

This project is for something I have been curious about trying for awhile. I ran across a vendor in Germany that uses an aeration tube to strip any excess CO2 from the effluent coming from one of their calcium reactors. Their reactor design operates in saturation mode, like my ACR CalRx does. This style of reactor uses the saturation point of CO2 to control how much CO2 is added to the CalRx water column. Other popular designs like Dastaco and Deltec also operate in saturation mode. This method removes the variable of setting the CO2 rate correctly. Bubble count / tuning / pH control, etc. all becomes irrelevant once you take the approach of adding CO2 until no more will dissolve.

The expectation is that the effluent of saturation CalRx's will contain excess CO2 within the effluent. This project is to alleviate this possibility.

I decided to add an aeration tube to my ACR along with a air separator / settlement tube for removing the air that is used to strip the CO2 from the effluent. This is the basic design that the German CalRx vendor uses.

I ordered in the needed parts to build both parts from 2" PVC. I went with schedule 80 grey to match my ACR CalRx. There is no pressure involved, so schedule 40 is fine, and opaque tubing would be OK as well, but being this is a project, I went with clear PVC so I could see what is taking place inside.

Here are the parts I ordered.

The plan was to use the clear PVC length for a 12" air separator / settlement tube and the remainder of the 36" tube to for the aeration tube.

I often hurry the actual build, which can lead to mistakes, but I managed to catch and avoid making any fatal mistakes during the gluing process.

The completed units are shown here. Concerning mistakes, I did not tap the 1/4" holes deep enough resulting in the push fittings not screwing in to full depth. After noticing the issue I went to re-tap the affected holes and in my haste, did not notice that I had cross threaded the tap in the air vent hole. After realizing it was cross threaded, backing it out, and screwing it in again cross threaded, but in a different orientation, I started to get concerned. I looked at the hole and the tap was chewing through all the material in the multiple insertion and removals of the tap, miss threaded 3 times. I thought for sure I had wrecked the part. I carefully made 1 more attempt at threading the hole with the tap held vertical and plumb to the hole. I tried screwing in a fitting and could just engage the threads at the deepest part of the hole. This would likely not seal the fitting properly, so I added an o-ring to the fitting. This seems to seal it fine with the o-ring. Even if it leaks, it will only be air higher in CO2 than the surrounding air (hopefully).

Because I wanted a push fitting inside the aeration tube, I added a couple of o-rings to try to prevent saltwater from reaching the metal in the push fitting connector. This fitting is in the airspace above the water level in the aeration tube, so we are mainly trying to prevent splatter from contacting the metal gripping ring.

This is the completed build attached to a stand I made to hold the equipment I replaced my factory controller on my ACR CalRx. The top pH controller is used to control the akalinity by disabling the reactor when my Alkatronic indicates the alkalinity level has risen above the setting on the pH controller. The bottom pH controller is for setting the pH of the effluent leaving the air separator / settlement tube (horizontal tube in photo).

A picture of the backside of the stand holding all the adapters and power relays. While putting it into operation and carefully checking for leaks, I noticed that if any leaks were to occur, the power bar mounting puts them directly under a potential source of leaks. Not the best idea, so I will look to improve this in the future.

A close up of the 2 pH controllers on the stand. The Clippard valve in the photo is for controlling the CO2 to my ACR CalRx. That valve along with a Masterflex replaces the factory controller that came with the reactor.

I have brought the unit online. I have a tiny leak in the pH probe holder. I used one of the 1/2" NPT fittings from electrical suppliers. I used the flat o-ring that came with the fitting, but it seems to have a slow leak, so I will need to shut it down and tape the threads to seal it.

The initial results are interesting. The pH of the effluent I filled the aeration tube with was 6.1 pH. I set the controller to 7.3, or where I thought 7.3 would be on the scale, and enabled the unit. The air pump turned on and ran for less than 60 seconds and then turned off as the pH had reached 7.4. I was a bit surprised at how fast the pH was raised. I was expecting a slower process, but the fine bubbles from the air pump did it in seconds instead of minutes or tens of minutes.

This is now in use on my tank, but the tank is a small frag tank I am using to test equipment for a larger upcoming build. So the effluent rate is so slow (0.8 ml/min), that the air remains disabled for long stretches of time. I have only managed to catch it activating once for a few seconds and then shutting down. I would expect that in a higher demand situation, it would toggle on a more regular basis.

To track any effect this is having, I have been tracking the concentration of CO2 within the tank for the past several days. I use the Marine CO2 Level Calculator from Hamza's Reef to do this. I just put the unit online less than 24 hours ago, so I am still collecting up the initial data.

I might have to remove some of the other elements that I have in place to deal with the CO2 within the effluent to give the aeration tower more dissolved to CO2 work with. My ACR currently feeds a Geo 618 with no CO2 hookup. The Geo helps to use up any excess CO2 within the effluent. The Geo is currently running with 6.16 pH, just based on the effluent coming from the ACR. I also have an 8" Geo kalkwasser reactor running to again use up excess CO2 within the tank. Both of these units may be competing with the functionality of the aeration tower and I may need to remove them to give the aeration tower something to solve, lol.

My tank runs between 8.0 and 8.2 pH on a daily basis now. I am hoping to pump up these 2 ranges by 0.1 pH on a daily basis. Let's see what happens.

Dennis

 

[lapin]

Nice write up

 

[Dennis Cartier]

Ok, I have some preliminary results from the project. The aeration tube has only been active for about 48 hours, but I 'think' I see an effect. There is a little bit of a complication in interpreting the data though.

Without considering that it may complicate collecting data later, I trimmed and removed most of the cheato in my fuge barrel that had become mixed with GHA. Unexpectedly, this shows up in the graph. I am a bit of a noob on Google Sheets, so I was unable to label it, but it occurred around the 4th spike from the right (July 31, 2021), which has the first 'flattened' appearance.

I then put the aeration tube into service 24 hours later, which is during the next flat point. Over the next 48 hours, you can see the blue line, which corresponds to CO2 in dissolution within the tank, has started to decrease.

The million dollar question is if I had not removed a large portion of the cheato, would the aeration tube still be showing the same decrease in CO2 and rise in the low point of the pH?

Interestingly, the low points for CO2 on the graph from before I put the aeration tube into service appear to correspond to when I put fresh kalk in the kalk reactor. The most recent dip in the CO2 when the aeration tube was online, did not correspond with any kalk addition. I am holding off adding kalk to prevent the change from skewing the results of the aeration tests.

Dennis

 

[Dennis Cartier]

An update on the aeration project is in order. I have been monitoring the dissolved CO2 level and pH of the tank after the inclusion of the aeration tube (updated chart below). In the graph, I added a Kalk line to show when Kalk is being used and when it was refreshed (spike). I also added a Fuge Air line to track the effect of removing the outside air being bubbled into my fuge. I plan to disable this in the future to gauge if the aeration tube can pick up the slack.

What I have concluded is that aerating your CalRx effluent to a preset pH is an effective way of limiting the tendency of the pH being dragged down by CalRx usage. However there is an issue with my implementation. The dKH line after the aeration tube was put into place shows the issue. The graph for the dKH is more 'spikey' after the aeration tube was put into use. The reason for it is that the drain for the settlement tube is not dripping slowly and continuously as expected, but is instead building up a reserve of effluent and then releasing it all at once in a siphon process. This is resulting in a sudden surge in dKH and depending on how close it occurs to the 6 hour alk test performed by my Alkatronic, causes a spike and then the CalRx gets shutdown for 6 hours for being too far above the target alkalinity. This both makes the graph rough and spikey and I am sure my corals are none to pleased either.

On august 13th and 14th, the timing worked out and the effluent dumps were fat enough away from an alk test to allow the system to operate for 2 days straight, and the graph shows the reduction in CO2 and boost in pH (they cross each other in the graph).

The way I implemented the drain was how the German CalRx manufacturer appeared to structure theirs. I am going to go back and rework it. This will give me an opportunity to seal the ragged hole that I messed up with too many misaligned tap attempts, and tap a new hole for a 3/8" fitting in the center of the end cap. I am hoping that going to a 3/8" tubing for the drain will allow the effluent level to slowly rise until a tiny flow is achieved and not work in a siphon fashion like the old implementation.

I also plan to lengthen the tubing that connects the overflow to settlement tube. Currently it is only a few inches long and means removing the settlement tube leaves it tether to the aeration tube with no slack at all. Hopefully I remember to seal the probe holder fitting to remove the possibility of a leak. The current leak seems to have self sealed, but I would rather remove the chance of it restarting entirely.

So that is the update, working well but not perfect (yet).

For some reason the updated chart only shows when you click to view.

Dennis

 

[Dennis Cartier]

I sealed off the badly tapped hole in the sediment tube and tapped a new 1/4" hole in the center of the end cap instead. I switched to using a 3/8" fitting and right angle stem to push adapters instead of the 1/4" ones I had used previously. I am hoping the 3/8 versions flow more easily as it is only gravity fed due to the vent hole bleeding off all pressure.

If the spikes in the alkalinity in the graph moderate after this change, then it will have accomplished what I was hoping for.

I have allowed the kalk saturation to weaken in the meantime to see a weaker kalk saturation would help to eliminate the alk spikes. I can do a kalk refresh in the next few days which will help to test the moved drain hole to see if the alk spikes are more to do with the drain choppiness or the alk being pushed too high by kalk saturation and the effluent being toggled off frequently by the Alkatronic.

Dennis

 

[wtac]

AquaCare CaRx

For the size per rated system, phenomenal and novel product.

Nice to see a DIY approach with points of monitoring and control.

 

[Dennis Cartier]

AquaCare CaRx

For the size per rated system, phenomenal and novel product.

Nice to see a DIY approach with points of monitoring and control.

Ya, I stumbled onto them when I was researching Schuran reactors. I thought their design was so neat that I lifted the aeration feature. For saturation style reactors like my AE ACR, it is a handy addition. I also like that they used PVC for every part of their reactor. Though they seem to be switching to acrylic

Dennis

 

[brett.sizeland]

Hey Dennis how has this been going for you? still working well?

Are you able to post a photo and markup the inlet and outlets? keen to make one for myself as I run a Deltec CRTT and having issues with it suppressing my pH a lot.

 

[Dennis Cartier]

Hey Dennis how has this been going for you? still working well?

Are you able to post a photo and markup the inlet and outlets? keen to make one for myself as I run a Deltec CRTT and having issues with it suppressing my pH a lot.

Hi Brett.

After running it for awhile, I do have some feedback on it. I run an Aquarium Engineering ACR, and like the Deltec it runs at saturation. So I built this to help strip the excess CO2 in the effluent.

Recently, I made a change to my DIY controller on my ACR that allowed me to select the internal pressure I am running my reactor at. After operating my ACR at 8 PSI, I found that the effluent was super saturated with CO2, akin to being carbonated in fact. Think Soda Stream, lol. What I found is that CO2 was falling out of suspension in my secondary chamber, which is an old Geo 618 CaRx with no CO2 feed hooked up. So I dialed the PSI back to 5 PSI, which has helped to reduce the amount of CO2 getting passed along to the secondary.

I don't know the exact pH my ACR is running at, but I expect it is in the high 5's (~5.7 - 5.9). The pH in my secondary hovers around 6.1, and drops to high 5.9's (E.g. 5.97) the day after a venting, and then slowly rises back to 6.1. If I don't vent once a week the pH in my secondary slowly rises as my effluent weakens.

After the effluent leaves the secondary, it goes through a 'magnesium tube'. Essentially a small 2.5" inline refillable cartridge containing ReMag. Then it flows into the bottom inlet of the aeration tower.

You can see the bottom 1/4" inlet at the bottom of the tower and the exit at the top in the photo below. (sorry no markup, I can't remember how I marked up photos in the past in Google Photos)

Once the effluent gets into the tower, it is now at about pH 6.5. Going through the ReMag raised it by 0.4.

Does the aeration tower work?

Yes, absolutely, it raises the pH quite effectively and I can select the pH of the effluent leaving the tower using the pH controller controlling the air pump. However there are caveats (aren't there always?). As the air is being bubbled through the tower, the air displaces effluent, so you do get some surging in your effluent stream where 'extra' effluent is pushed out, and once the air turns off, less effluent will be pushed out until the effluent flowing in catches up.

A bigger issue is that as the pH is being driven higher, it causes CaCO3 to precipitate from the effluent, covering the internals of the aeration tube in a white film. The precipitation lowers the strength of the exiting effluent, losing a bit of the supplementation that the CaRx has been working hard to provide, and in the process removing all the excess CO2 that may be present it the saturated effluent.

Unfortunately, it also precipitates on the pH probe, eventually affecting it's performance. This requires the pH probe to be 'de-calcified', which entails removing and cleaning it. This step, is the one area where my design leaves a bit to be desired, as removing the pH probe, requires lowering the water level inside the aeration tower to below the probe so the probe can be removed, cleaned, re-installed, and then adding the removed water back to cover the probe. This process is a bit of a pain, and is the one area that I think can be improved.

One improvement that I have already made to the design, is that I added a second 1/4" inlet at the bottom of the tube, directly below the pH probe, to slowly pump air into the tube to help with mixing while the air pump is off. This helps with the pH probe tracking the internal pH better and not suddenly jumping when the unmixed effluent eventually reaches the probe. I added a second head to my Masterflex that has an inlet open to the air and air bubbles are slowly released to flow up the tube and provide a bit of circulation.

Another issue that has arisen is that I used a Murlok style check valve, thinking it was good enough to protect the air pump, and recently found my air pump full of water. Gah. So be sure to use a better check valve (than I did) and mount the air pump above the aeration tower. Not the easiest thing to do with it's height though.

Would I build it again?

The one thing I don't like, and mainly because I am lazy, is the maintenance required for the pH probe. Having to remove the precipitation to keep it accurate is unfortunate. However, having the probe in place has shown that simply doing a slow flow through media, can significantly raise the pH of the effluent. The Geo 618 active re-circulation secondary chamber, raises the effluent to 6.1. Flowing through the much smaller, passive, inline ReMag tube, raises the pH to 6.5. So I am curious if adding another inline tube with media would get another bump in pH and get the effluent closer to the target pre-aeration tower.

Another idea I have been thinking of is if it is possible to eliminate the need for the pH probe in the aeration tower, by adding a duty cycle timer to the air pump. Essentially toggling it on and off at a select-able rate. The factory ACR controller used such a timer, where you could set the on and off periods of a square wave. I have re-tasked this hardware to toggle a 120v outlet. Using this I might be able to find a reasonable default to adjust the pH up without depending on the pH probe. It would of course be flow dependent. An increase in flow would require a new setting for the air pump duty cycle timer.

You may also be able to automate this using a controller (E.g. Neptune Apex) that adjust the duty cycle of the air pump based on the tank pH.

What I have found is that, another pH correction feature that I employ, has a much bigger effect than the aeration tower. I have a needle wheel skimmer pump, being fed from outside air, in a fuge barrel that runs 24x7 and it raises my pH the most of everything. When the pump gets clogged with algae, my pH drops by 0.1 - 0.2. Unfortunately it is not really conducive to the fuge being a fuge as the wall of bubbles decreases light penetration a fair bit.

So would I build it again? Before answering that, I want to test added inline media cartridges to see if I can get the effluent closer to, or over 7.0, without the benefit of the aeration tower. If so, then that would be a much simpler solution for stripping the excess CO2. I will update this thread when I have that answer.

 

[Dennis Cartier]

Ok, I added another inline media cartridge, filled with ARM coarse, after the existing cartridge that is filled with ReMag. It had no effect on the pH of the effluent. So no joy.

I am planning on taking my kalk offline, I am getting short on Masterflex pumps, and I need to have my CaRx set to handle all supplementation for vacations. So I will be replacing the air pump that got damaged by the failed check valve and will be using the aeration tower to strip the CO2.

However, I don't want to have to depend on the pH probe to control it. The precipitation issues are annoying with the probe, so I will be employing a periodic timer to toggle the air pump off and on and just use the pH probe to get an idea of the effect of the timer setting when initially setting it up.

 

[Dennis Cartier]

After using the periodic timer for a few weeks. It seems to be a good solution compared to relying on a pH probe. With no air pump, the effluent being added to the sump was 6.6 pH. With the air pump being engaged for 90 seconds every 15 minutes, the pH of the effluent was 6.8 during the day and 7.2 at night. I slow my CaRx flow rate at night, so that is why the night reading is higher at night.

I am automating the dosing of TM A- & K+ elements tied to the amount and strength of effluent dosed, so I recently measured the dKH of the effluent being delivered to the tank. I found the effluent to be 90 dKh. Still fairly strong, even with the small amount of precipitation the aeration tower causes.

With kalk removed, my tank is running high 8.3's during the day (with the occasional 8.4), and mid 8.2's at night (with the occasional high 8.1).