I've been running a CPR BakPak (original model, now referred to as the BakPak1) for over a year and have learned a few tricks for "tuning" it that perhaps others will find useful. These comments are only for the BakPak1 and may not apply to the BakPak2 (newer model) because I have not worked with those. However, my understanding is that the 2 is very similar to the 1, so most of this should apply.
This document is divided into 3 parts:
Note: this part was written before I did the airstone modification.
Although the BakPak is a "plug-and-play" skimmer, there are some things you can do to keep it working at peak efficiency.
First is the adjustment of the skimmer cup. Normally, the flat, bottom lip of the cup neck (the curved part that collects the bubbles) should be 1/16-3/16 inch above the top of the water in the column. This will result in a nice "dry" foam and a thick skimmate. This is where the cup should be adjusted most of the time.
If your skimmer output is temporarily low due to some condition in the tank (like adding certain chemicals or putting your hands in the tank), or if you want to pull a thin green skimmate as fast as possible regardless of salt loss (like maybe because you have some "chemical emergency" in the tank) you might want to lower the cup so that the top of the neck (where the neck meets the base of the cup) is at or just above water level. This will fill the cup quickly if the skimmer comes back "on line" so keep an eye on it when you set it this low.
More useful in day to day use is adjusting the air supply. While many recommend removing the silencer from the end of the air input tube, I found that this was only appropriate under some conditions (plus it's noisy). A better solution, in my opinion, is to buy an airline needle valve at the aquarium store. Regular "lever" style valves can also be used, but will not provide as fine a control. I found one for $0.59, so it's not an expensive modification. :)
Remove the silencer on the end of the airline and install the needle valve in its place. Then adjust the valve to produce the most "opaque" amount of bubbles in the column. I found that this simple trick -greatly- improved the day-to-day output of the BakPak.
Under certain conditions the bubble production can be so high that some will travel all the way through the skimmer and end up in the tank. I have found that this is usually a temporary condition (an hour or so). If this is a persistent problem for you, see the FAQ portion of this document.
Sometimes the valve will need to be all the way open to get the best bubbles. In rare (and temporary) conditions even this is not enough and the valve should be removed temporarily to allow unrestricted air passage. However, most of the time on my tank the valve needs to be very nearly -shut- for best bubble production. Every tank will be different, of course, but I have found that by playing with this valve I probably double or triple average skimmer output over time.
I don't want to give the impression that using a needle valve requires constant "fiddling". Mine normally remains untouched all week. But, on the weekends when tank maintenance is performed, or when new corals are added, I sometimes have to adjust the valve for a few hours to keep output up or reduce it.
One final trick has to do with cleaning. If you take the valve off and blow through the airline you will effectively "backflush" the bubble generator on the pump. I do this once a week. It sounds like it "stalls" the pump, so don't do it for too long at a time.
Once every 3 or 4 months I take the pump apart and clean it. In case it's not obvious how to do this (it wasn't to me), here's how. The pump end, where the tubes attach, is the only piece you need to take off. The cover on the opposite end does not need to be removed.
Remove the outer cover on the outlet end of the pump assembly. Careful prying may be necessary. Rotate the round plate where the airlines attach so that the two nipples are oriented straight up and down. This will allow some "flat" areas in the serrated edges of the plate to line up with the retainer clips, which will allow the pump face to be pulled straight off. It can be a tight fit, so be firm but careful. Clean the magnet cavity, magnet, and impeller and reassemble. After you put the pump plate back on be sure to rotate it somewhat so that it does not come off accidentally.
Adding airstones to the BakPak can double or triple its output in both quantity and quality. "Quality", in this case, being judged by darkness, thickness of foam consistency, and smelliness. The increase in output should help any BakPak owner who is pushing the limits of the skimmer, and may allow it to be successfully used on tanks larger than are usually recommended for the BakPak.
You will need one or two smallish airstones. I use 2 "limewood" airstones that are about 1" long that I found at the local fish store (LFS).
You will also need some airline. This should be stiffer than ordinary airline, in my opinion, to avoid kinking. I used Tygon, I believe.
You will need a medium-sized air pump and a way of adjusting it. I used a Hagen Maxima-R which was convenient because it has a built-in rheostat for adjusting the pump output. I normally run it wide-open, though, so I would not use a pump smaller than this unless you are only using one airstone. For conventional pumps you could use an air valve to adjust the air flow.
Run one airline for each airstone down the outlet side of the skimmer box, under the divider, over the center divider, and then back under the divider into the inlet chamber. Keep pushing them through until they come out the top. Now put the airstones on the lines and pull the lines so that the airstones go down to the bottom of the inlet chamber. Hook the lines up to an air pump. You're done. :) In case you are using the CPR bubble trap accessory and are wondering, yes, there is sufficient clearance for the airlines.
Adding airstones to the BakPak will change its characteristics so much that the tuning suggestions given earlier no longer apply. Instead, I suggest that you raise the collection cup by lowering the o-ring as far as it will go and still stay on. This runs the cup about 1.5" higher on mine than I did without the airstones. Now use the adjustment on the air pump to adjust the foam level. With my setup I normally run the air wide open. I continue to use the built-in BakPak venturi in addition to the airstones and I still adjust the same as I did before. Turn off the air pump to allow viewing the output of the venturi for adjustment purposes. On my system the venturi+airstones is about all the skimmer can stand without drawing green water under normal circumstances, so this suggests that a pump with the output of the Maxima-R is sized just about right.
Dark skimmate will now collect on the upper walls of the inlet column of the skimmer as well as in the collection cup. This must be cleaned when the collection cup is cleaned, but must -not- be allowed to flow back into the aquarium. For mine I cut down a small piece of sponge so that it would easily fit inside the inlet column and use that to swab the skimmate out.
I have noted that the BakPak is a lot more "touchy" about adjustment since putting in the airstones. Little things that disturb skimmers like feeding the fish, putting your hands in the tank, or dosing some additives seem to change the output level much more than it did before. If the skimmer goes into "overproduction mode" it is now capable of drawing a significant amount of water out of the tank and on to the floor.
All in all, this modification is HIGHLY recommended.
For those who haven't seen one, the BakPak is a hang-on protein skimmer produced by CPR, Inc. Here's their website:
Creative Plastic Research. The BakPak is a venturi skimmer that comes with a "regeneration" or "rejuvenation" venturi arrangement. This is sometimes called an "RVT" style skimmer. In the case of the BakPak, the RVT head is mounted on a Rio 600 pump (which is included with the skimmer). CPR makes a model that is virtually identical to the BakPak, but for in-sump use, called the SR2. They also make a number of other, larger, air-powered and venturi skimmers.As I understand it, not having seen a BakPak2 in person, the differences are these: the BakPak2 has a black tube, instead of a clear tube, connecting the pump outlet to the skimmer inlet. This is intended to help prevent algae growth in the tube. The biggest difference between the BakPak 1 and 2 is the arrangement of the skimmer outflow. On the BakPak1 this is a "waterfall" style, like a traditional hang-on power filter. On the BakPak2 this has been changed to an adjustable outlet pipe that runs under the surface of the tank. I believe this change was made to address comments about salt creep and noise with the original setup. On my BakPak1 the noise does not bother me, but I definitely have some trouble with salt creep.
CPR rates a BakPak for tanks up to about 60 gallons. My own experience and that of many others seems to bear this out as a reasonable number.
The BakPak does a super job on tanks in the 15-30 gallon range and is quite popular with microreef owners. On larger tanks the BakPak is more controversial. The great majority of people using these on tanks in the 40-65 gallon range are satisfied, especially those who have done the airstone modification. Some people use these skimmers on really large tanks, into the hundreds of gallons, but then some people run systems with no skimmer at all. The consensus opinion on this is that a BakPak is not sufficient for most larger tanks.
I do not find it noisy. The most annoying noise is from the venturi airline inlet. This can be noisy if the filter/silencer is removed, but attaching an air valve, as outlined above, cures this. There is some gurgling noise from the skimmer outlet but I do not find this objectionable. The changes on the BakPak2 are supposed to reduce this. I consider the BakPak quiet enough for use in a bedroom aquarium. Your tastes may differ.
I like mine. It traps the bubbles. If you remove the media from the outlet side of the skimmer you will probably need the bubble trap or some other method to keep excessive bubbles out of the tank.
Yes. This really increases the efficiency of the skimmer. Extracting the skimmer water from the surface will help any skimmer.
This is usually caused by the pump face coming loose. If it comes just a little bit loose it will leak air bubbles into the tank. See the section on Tuning the BakPak1 for instructions on how the pump head should be installed.
Several things can cause a BakPak to put excessive bubbles into the tank water. Here are some things that can help fix this:
If you have removed all media from the outlet box, consider getting the bubble trap accessory from CPR. This is fabricated acrylic thing that goes in the outlet box. It takes up about all the room, so you generally can't run media, heaters, etc., in the outlet box if you use the bubble trap. DIY folks can try other methods that will break up the bubbles in the outlet without adding significant restriction.
If the water level in the tank is too low, or if the water level of the outlet side of the skimmer is too high, it can increase the tendency of the BakPak to put bubbles in the tank. Adjust as required. :)
If the overflow is from the outlet side, and you have a BakPak1, take out that little sponge thing on the outlet. It can cause the water to back up enough to raise it above the edge of the outlet lip. This can also be caused by adding a lot of restrictive material to the outlet box, again causing the outlet water level to rise too high.
If the overflow is from the skimmer cup, be sure you have it adjusted so it is not pulling out too "thin" a skimmate.
If the skimmate is thick and overflows the cup, empty your cup more often. :)
If the foam is thick and it insists on pushing the lid off the collection cup, try adding some weights to the lid. If that is not enough, enlarge the holes in the lid. If -that- isn't enough perhaps you should consider another skimmer? :)
I don't claim to be an expert, just a hobbyist. This is all just my opinion and based on my own experience. If something else works for you, great!
BakPak and CPR are, presumably, trademarks and copyrights of Creative Plastics Research. They have no connection with this document and I have no connection with them other than being a satisfied customer.
Copyright, 1998, Dave Bird. Please do not reproduce without permission (which will normally be granted on request).
Hope this was of at least some interest.
Dave Bird
With many thanks to Dave Bird. Thiel Techologies 3/3/98