Concentration problem solved

The first thing i did in June was to test the hypothesis about nutrient limitation being the cause of my low algae output. Since I could measure actual concentrations of nitrate and phosphate, I assumed that these could not be the problem. The problem had to be something in the Seachem Flourish. What if something there was unbalanced, taken up unexpectedly by some organisms, broken down by bacteria, or simply skimmed out? So I doubled the dose, and instead of adding a weekly dose once a week I added a third daily dose 3 times a day. This had a great effect. The blooms now grew to much higher concentrations, and lasted longer. A diatom bloom gave up to 5 grams of food per day. A bloom of small green algae gave more than 2 grams per day. Small algae are much more visible, per weight unit, than larger cells. This caused the water in the display tank to become completely green during the bloom a small cells.

Another concentration problem

As soon as the problem with low concentrations was solved a new challenge popped up: High concentrations in the display tank. The skimmer was very poor at removing the small 2 micrometer green algae. So they accumulated until the concentration in the display was almost as high as in the refugium. I decided to empty refugium and switch off the lights completely. But it still took 2 weeks for the display tank to be reasonably clean! So the skimmer performed extremely poorly against these small algae, and they survied and stayed suspened in the water for a very long time in the dark. So this is a challenge I must look into. One of the ideas currently is to check is the algae will disappear faster in the display if they are killed by a UV filter. I have two of those lying around from old days. I am not enthusiastic about that, but reasonably clear water in the main display is important.

Artemia

I have been thinking about growing artemia naupli in the refugium to get zooplankton. The plan is to add a certain amount of resting eggs every day, let them hatch in the refugium and feed until they were washed into the main tank. I was assuming that artemia eggs would sink. That was wrong, most float in the beginning. This would cause them to go into the overflow. So during my small test period I let them hatch for two days in a glass of refugium water and then added them to the refugium. I had two such glasses standing and added one to the refugium ever day for about a week. I saw lots of artemia naupli in the refugium, and I could see clearly that many had grown significantly. But I never observed any in the display tank. I didn't do any measurements in the short period of the experiment. Later I plan to add the eggs in a feeding ring to make sure they don't go in the overflow before they hatch. Then I will start doing concentration and biomass measurements.

Collection trips

I didn't find anything special the last month. In fact, I had to take my sea cucumber back to the ocean because it wandered around too much, and wouldn't open up and feed properly. Still, here are a few pictures from the trips I had. As you can see, there is a great blue green Emiliania huxleyi bloom in many places. Combined with heavy summer algae growth it gives the underwater environment a strange look.

Free diving gear

I finally bought myself a full free diving gear! I have only given it a small test so far, and it worked well. But the water is extremely murky at this time of the year. I think it is Emiliania huxleyi that is blooming in most areas around here. The plan is to take a course later in the summer. Finally I am taking a step below the tidal zone!

Plans ahead

I have summer vacation now in July, but will probably be busy with other stuff. So there probably won't be that much happening this month. The refugium is empty right now, and I may wait until late July before filling it up again. In August though, I hope to get done lots of free diving, and new experiments with feeding.