The first 5 weeks after restarting the refugium in April the growth was limited, with a few crashes. But then a bloom started, which has lasted ever since. So I am still confident in the phytoplankton capabilities of the refugium. In the display tank there is a bloom of bryozoa, or moss animals as they are commonly called. At least I think it is this kind of animals. The alternative is hydroids. Some crust forming bryozoa look a lot like small hydroids since they have organs that look, and function, much the same as polyps. They cover the left side wall, partly the right side wall, and many of the other exposed surfaces. They look like brown fur in some cases. I don't really mind them. I am thinking about introducing bryozoa eating nudibranch snails. I know what they look like, and I have seen them many times so it should be possible to find some.

Newcomers

I counted at least 120 blue mussels (Mytilus edulis) that were of an average size of about 2 cm and had grown entirely from larvae in the tank. The larvae were not consciously introduced by me. And there are also dozens of juvenile mussels in the refugium now. In addition to this there are dozens of adult rock borer clams (Hiatella arctica). So I decided to take the chance and introduce some clam predators. I chose two common sea stars (Asteria rubens), juveniles of about 5 cm diameter. And 5 dog whelks (Nucella lapillus), also young individuals of about 2 cm length. The dog whelks are white, indicating that they have a barnacle diet. But I hope they can readjust in the tank. So far I haven't seen the stars really much, they are hiding. The dog whelks are visible and usually fairly stationary. I haven't seen any indications of greedy feeding behaviour from any of the animals. I am considering getting a few more predators, and perhaps some dog whelk eggs. There are many of them now, and I believe they don't have pelagic life stage.

Zooplankton tank

As you may remember from last update, I mentioned that I was setting up a zooplankton refugium too. The work in that area is progressing well, even though there were some initial issues. I wanted double glass on this aquarium too. This time I wanted to use aluminium square tubes around the glass as a frame, to make sure the seal got completely moisture proof. But such tubes were impossible to get locally. I called various sources, and looked in every building store. 20mm square profile tubes were possible, but nothing smaller. I even thought of alternatives like using glued acryllic or SAN glass. After all, plastic foil is used as vapour barrier in buildings. But this was of course a bad idea since acryllic and SAN are not like polyethylene, they absorb water. And if they can absorb they can release it too. In other words, water travels through them, slowly. Finally I found a source of 15mm alu tubes: A local cheap shop called Biltema had a cheap aluminium laundry drying rack that was made out of 15x15 and 15x25 tubes! The 15x15 tubes were perfect, but only 60 cm long. The 15x25 were long enough, but too big and with holes. So I decied to cut the 15x25s into 15x15 U profiles a use them on the long sides. So only the short sides will contain desiccant, but that should be enough.

Next up was which glue to use. The MS polymer from last time was out. But butyl sealant, which is known to resist moisture penetration, was tempting. But when I read on the tube that it said "hardens by releasing solvent", I just didn't want to take the chance. So I decided to try solvent free epoxy resin. There are a few issues with this: First, the bonding strength between aluminium and epoxy. Second, and more critical, will thermal expansion and contraction cause issues? Epoxy is rather brittle. Allowing for movement is why one normally uses silicone to bond glass and metal. I happened to have some pieces of glass lying that I tested on. I sanded the aluminium with 80 paper and degreased everything. Small pieces could be broken off with tongs, but larger pieces were really tight. I even did some half hearthed thermal testing with cold and warm water. So I decided to go with this solution. One interesting thing I found when cleaning glass with acetone was that the acetone left a terrible residue when it evaporated. So it was completely useless for cleaning. I have no idea if it was the acetone itself or a pollutant dissolved in it that was the problem. Anyway I am very sceptical to using solvents for cleaning after that. I tried xylene too, and that worked better. I may go with only isopropanol next time. It is not a strong solvent, but water soluble. I have this rather nasty feeling that some of the dirt between the window panes has been because of solvent residues. I never felt that they were perfectly clean from the beginning.

Other projects

This isn't directly related to the plankton project: When I worked with laminating epoxy this time I started using some improved methods that I have found on the net. That made it much more enjoyable to work with. I measure the components using an electronic kitchen scale, and mix them in plastic glasses that are practically free. Mixing is by hand with sticks that can be bought for virtually nothing. So everything can be thrown away and there is nothing to clean afterwards. Also, very little air is mixed into the resin when mixing by hand this way. When laminating, the resin is poured onto the cloth, and pushed out with a rubber pad. This demands that the surface is horizontal though. But it creates a nice laminate, with little air. The laminating epoxy takes a long time to gel and harden, making the work relatively stress free. No solvent is ever needed, well except when spills happen, and there is very little smell.

I have long been playing with the idea of building aquariums the same way that boats are built. That is with a so called "sandwich construction" with fiberglass reinforced plastic (FRP) on the outside and foam plastic in the core. So foam plastic instead of plywood, which is normal with aquariums. This would give a very light weight, easier to build, and insulated aquarium. The problem is that structural foam for boat applications, made from polyurethane or PVC, is extremely expensive and virtually only sold within closed circles of professionals. But it turns out that solvent free epoxy is compatible with something called XPS, a type of styrofoam. XPS is much stronger than ordinary styrofoam and sold in building stores for cheap. So now that I have started to enjoy working with epoxy I have decided to do some tests to see if this is possible to use. I bought some XPS and started playing around with it. I did some bonding tests and found that epoxy would bind acceptably to roughed up surfaces. Right now I am doing bending stress and deflection tests. It will be fun if this can be used for something!