Allright, I finally have a thermometer. I ordered it online and it turned out to be way to small (not helped by the addition of the arcane Fahrenheit scale…). Anyhow, my water turns out to be 25 degrees (Celsius)! This is a couple of degrees warmer than I thought, and not exactly characteristic of British Seas. I will have to save money for a chiller…
I also bought a hydrometer (cheaper than a refractometer) to measure salinity. This was even more of a shocker, the salinity was literally of the scale! >40 g/l instead of the 35 g/l or so of ‘regular’ seawater!
I have recently started to change water more frequently, which means I have not been topping up evaporated water with distilled water but instead replacing this water of 0 g/l salinity with seawater of 35 g/l salinity. Stupid. Tomorrow I will take back distilled water from the lab for a good water change (gradual of course). My temperature and salinity values demonstrate that rock pool critters are quite hardy: all my fish and anemones seem to be doing just fine. However, who knows these high salinity levels might have caused problems in the aquarium for some of the seaweeds collected from the lower shore…
P.S.
Actually, recently one organism died a week after I put it in the aquarium, probably because of the temperature and salinity shock, the beautiful Dahlia anemone Urticina felina (not a very good photo):
An Bollenessor 