January 27, 2016

Ready for restart

I knew the summer of 2015 would be very busy, so I decided to take a pause in the project until I had more time. Now, almost exactly a year after the first start up, things are getting ready again. In my previous update I talked about building a filter. It is almost finished, with only one hurdle left to fix.

Why a filter?

There are two major problems with the system at the time: First, the phytoplankton tank doesn't produce as much plankton as it did in the first plankton project. Also, it is less stable. The benthic copepods don't bloom in such numbers as they did then. In the first project there was a continuously running skimmer. It also had ozone added occasionally. This clearly removed some organic materials from the water. It had good circulation and a bio filter in the form of the live sand bed. That removed organic material too. Other differences were higher temperature in the phyto tank, and the fact that I dosed nutrients manually. Last, but not least, it had addition of CO2. Let's assume that the organic materials are the problem: Is it the large amount of materials, or is it some more specific compounds that act as toxins? Assuming the last, the new filter should have a good chance of fixing the problem. The biggest problem in the second project is the lack of zooplankton growth, of course. But if some organic compounds are the cause of that, then the new filter could be the solution there as well.

Ozone granular activated carbon reactor

Finished ozone and granular activated carbon reactor being tested.

The new filter

The new filter is basically an ozone and granular activated carbon (GAC) reactor. I have seen a few professional ozone reactors on the market, but they were expensive, and I didn't feel that I understood exactly how they worked. So I didn't want to take the chance that they wouldn't meet my needs. The normal way to add ozone is to add it to a skimmer. But I wanted to make sure that the water was extremely well filtered by GAC before returned to the zooplankton tank. That meant having the water slowly rising up through a column filled with GAC. I also wanted good GAC filtration of the air. Achieving both these with the effluents of a skimmer is so hard that I decided to just build the whole filter from scratch.

Drawing of ozone granular activated carbon reactor

The filter is open to air at the top, a bit like a skimmer. Water enters the ozone chamber near the bottom and is mixed with ozone and air by a recirculating skimmer pump with needle wheel impeller. It then flows up through the GAC chamber, overflows and exits. The air continues out at the top. Before entering the main filter body the water enters a standing pipe next to it. The entry point is above the water level in the main body. This prevents any draining back to the tank when the feeding pump stops.

Ozone granular activated carbon reactor

Here it is almost finished.

Design of the filter

The inspiration for how to build this filter came mostly from my old Deltec APF 600 skimmer. A little inspiration also came from pictures of a type of american skimmer brand called Euro reef. These old skimmers really have a "home made" look. Most of the parts are standard tubes, sheets and PVC plumbing parts that are cut and glued together. The bulkheads going through the wall of the reaction chamber are standard PVC unions that are cut in half and rounded so that they can be glued onto the wall. On the Euro reef skimmers even the skimmer neck is taken apart with what seems like a PVC union. Earlier you couldn't get large acrylic tubes and needle wheel pumps cheaply. But today they can be bought online for a reasonable price. So it would be fairly easy to build such a skimmer. Since my filter has many similarities with a skimmer, that was really good news.

Deltec APF600 protein skimmer

My trusty old Deltec APF600 skimmer served as an inspiration for the design of the filter. I borrowed the pump for my filter since the skimmer is not in use now.

Ozone granular activated carbon reactor

I bought these two acrylic tubes on ebay for the main reactor body. They are 110mm diameter and 500 mm long. I cut them down to 400mm.


It was very easy to make bulkheads into the acrylic tube. I just took a PVC union for gluing and sawed off the end. Then I taped coarse sand paper to the outside of the acrylic tube and sanded the end of the union until it had the same shape as the tube. It took a bit of patience and care to do the sanding, bit it was not hard. There was then a rather large contact area for gluing the union in place. PVC glue works reasonably on acrylic too. A small stub of PVC was glued into the union and passed through the hole with a narrow fit. This strengthened the joint and held the bulkhead in the right place while the glue cured.

Ozone granular activated carbon reactor

Cutting off a PVC union and sanding it to get the right shape for gluing to the acrylic pipe. Notice the trick with taping sand paper to the outside of the pipe.

Ozone granular activated carbon reactor

Finished shaping a bulkhead with sand paper.

Ozone granular activated carbon reactor

Drilling holes for the bulkheads with a stepped drill bit.

Ozone granular activated carbon reactor

Bulkheads for skimmer pump are glued in place.

Chamber separator

To separate the two main chambers, ozone and carbon, I use a 110mm PVC union with a self made mesh plate. The plate lets through water and air, but stops the carbon from sinking down. The PVC union is designed for pipelines with up to 16 atmospheres pressure, so it is overkill for this particular job, to say the least. Still, without it it wouldn't be possible to change carbon in a simple operation, or reach into the ozone chamber with a hand for cleaning. It may have been better to use a 90mm union and pipe for the carbon chamber, and a 130mm pipe for the ozone chamber. Currently the ozone chamber feels a bit small, while the carbon chamber is a bit big.

Ozone granular activated carbon reactor

Separator plate and 110mm union.

Ozone granular activated carbon reactor

View from below.

Weipro ozonizer ET-50 Ozone generator

My ozone generator.

Ozone granular activated carbon reactor

Complete filter setup with ozone generator on wall.

Design weakness

I have only found one real design weakness with this filter so far. But it was easy to fix: The exit overflow hole at the top of the carbon reactor is 32mm. I assumed that would be plenty for the relatively low throughput of the reactor. But because of the small size of the carbon pellets the hole was almost completely without flow. Another mistake was that it was attached to the removable part of the union. That meant carbon would fall out when I removed it. So I needed to make a larger barrel shaped drain in the chamber itself.

Ozone granular activated carbon reactor

This "grate" got clogged with carbon and didn't let out enough water.

Ozone granular activated carbon reactor

Here is the solution. This is sitting inside the carbon chamber. Picture is taken before the insect net was glued on. It has plenty of surface area.

Pump problems

I borrowed the pump from my Deltec APF600 skimmer for this filter. But there was a problem with it: It didn't start without help. I needed to blow into the air tube to get it running. That was a big problem since it was supposed to be turned on and off 6 times per day and run for 15 minutes each time. So I bought a very similar pump from China on aliexpress. But that pump was either very bad quality or it was too powerful for the narrow intake tubing in my setup. Probably the latter, since it worked better with full opening on the air valve. Anyway it made a rattling sound, perhaps some sort of cavitating. So I couldn't use it. The only solution was to use the old pump and let it stay on permanently. The feed pump and ozone generator will only run for 6 times 15 minutes though.

Ozone granular activated carbon reactor

This pump didn't work in my installation.

New dosing setup

The way the dosing pump was installed was very impractical. So I made this convenient little rack. The ends of the hoses are now under water to prevent risk of nutrients overflowing out of the refugium too fast.

Bubble magus dosing pump

More practical dosing setup. The Y splits are there to make sure the lower part of the tube (under water) is empty. Otherwise saltwater and nutrients will diffuse up and down the tube in their own tempo. Probably not a problem, but Y not :-p

Plans ahead

The filter has been operating with freshwater for several days now. It seems to be working fine. But the foam will be different with seawater, so issues could still arise. But I am optimistic. Just starting up as soon as possible is the plan now. Then I will take it from there one step at the time.

Back Home