Coldwater marine aquarium Blog 2007 September
9 September 2007

Wavy motion

My sister with family was here last Sunday, and they thought the wave motion of the green algae was really nice and relaxing to look at. They liked the tank. Here are some pics that try to illustrate it. The tank looks pretty good right now.

Algal growth and water chemistry

In the beginning of the period, around 10 of August, there were lots of nitrogen nutrients in the water. I measured 2 mg/l of ammonium and 10 mg/l of nitrate. The growth was great. The pH was 9.0 according to my meter so I decided to add CO2. Still I couldn't get it down. So I set in 2 yeast bottles and let them run continously around the clock. Still no particular reduction. But the growth was absolutely enormous. The Enteromorpha, Ulva and Porphyra grew very fast, so did the brown thread algae. The Enteromorpha also settled on many new locations and grew there. I love that algae because it competes with the brown thread algae and is not epiphytic. All the other algae also grew, both the kelp and all the various other browns, reds and greens that I have in smaller numbers. They grew very slowly in comparison. It turned out that the pH meter was wrong! The pH was correct to begin with and now it was 7.8. I bought calibrating liquid and a pH measuring kit for control. I should be safe in that area now.

At this point I was convinced that I would never be able to turn my tank into a nutrient poor environment in terms of nitrate and phosphate. I didn't even bother to measure those for days. But I was worried about other nutrients so I decided to go and buy some. First I bought iron rich trace minerals for FW aquariums and added that so that the iron level would be about 0.1 mg/l. The water got yellowish from that, probably added too much. Then I bought a very nice chemical package called the balling method. This package is supposed to contain all nutrients that a reef tank needs. Combine that with iron and I feel pretty safe that all is there now. The KH was 16 degrees though, because there was carbonate in the balling and I had added lots against the pH before, ugh. But a water change fixed that.


These nice red algae are growing in various spots. Not sure if they have spread by breaking off and reattaching or if they have had real reproduction in the tank. I wonder if the genus is Ceramium.

Then something funny happened. I measured the nitrate, and that pink color just didn't show up. It took a few seconds before it dawned on me, but there just wasn't any nitrate anymore. No phosphate or ammonium either! So all of a sudden I had a realistic low nutrient environment in my tank! Not sure about what to do with this new situation yet. Add nitrate and phosphate, or just see what happens? After all there is plenty of ammonium being produced all the time, sometimes I can measure small amounts. But I am worried that only the bad algae get the little nutrients that are present. Maybe there will be more nutrients as the days go shorter. Shorter daylengths has been shown to stimulate growth in kelp.

Black Goby

Black goby (Gobius niger). Deeply involved in the everlasting bickering about who is in charge of the best spot on the sandbed.

Added two black gobies (gobius niger). They seem to do fine just like the other fish. I also recently added 2 small pipefish. I was worried that the current was too strong for them. But they seem to manage that all right. They use the tail to attach themselves to algae or drift slowly around with the current. It doesn't seem to stress them. Haven't seen them eating anything so I hope they find something. After all the wrasses don't eat any of the food I feed either and they are still the fastest growing of the fish. So it is possible that they will find something in the tank. For example, the upper layers of the sand bed is full of small crustaceans.


Pipefish (Syngnathus sp.)

Hair crab

Hair crab (Pilumnus hirtellus)

Visited a very fine location on the islands to the west. At low tide I could lift up rocks in a kelp bed at a medium exposed area. Incredible place! I actually found 2 new crab species that I have never seen before. That was cool. They were both small, but the claws of one of them were enormous in comparison with the body. I didn't dare taking any of those. I didn't find out what species it was either. The other was hair crab Pilumnus hirtellus. They are a small species (about 2 cm carapace) and they had small claws, so I took the chance and brought 2 specimens home. They immediately went into hiding and haven't appeared since. Later I also found out that the claws will probably grow rather big compared to the body size. But at least the crabs won't be big enough to start pushing the rocks around!

Dahlia anemone

Dahlia anemone (Urticina felina). These like to hide, they squeeze themselves under rocks or bury in the sand.

Possibly Sagartiogeton sp.

Gammarus burrow

Here you can see the burrow of a 0.5 cm Gammarus amphipod. They seem to lie in these burrows fanning water through them with their feet. Maybe they are filter feeders. I thought they were detrivores. Maybe a combination.


Hitchhiking crab. Probably a common shore crab (Carcinus maenas).

Thoughts on kelp

I've done some reading about algae and nutrients here in the northern regions. There were some very interesting things that caught my attention. Consider theses statements: Kelp doesn't like heat. Kelp growth is stimulated by short daylengths. Kelp has its main growth season in late winter and spring when a new thallus forms on the laminaria species. It stops growing in summer. The funny thing is that the phytoplankton spring bloom that uses up all the nutriens starts in May. Pretty late. Why can't phytoplankton bloom earlier? The reason it doesn't start before is that in order to have a real immense bloom you need a stable upper mixed thermal layer. This doesn't form until the water gets heated in spring. Before that phytoplancton gets mixed into the deep at such a rate that a bloom cannot occur. So, this should imply that there is a window of oportunity in late winter and early spring where there are nutrients, light and clear water. The kelp is thus adapted to have its main growth at that time. The water is very cold at that time, and daylengths are relatively short. These are just my thoughts at the moment, I will try to read more about it.

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