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Salinity and Temperature

By Craig Bingman and Rob Toonen. Posted to Reefkeepers emailing list, Wednesday the 2nd of February 2000.


Just the thing I was thinking about this morning on the way to work. I have a 150gal tank 5x2x2 and have a 1-2 inch live sand bed, and 125-130 pounds of Brazilian and Marshall island live rock. I have no corals but do have 2 (6-8 inch) angles, 3(4-5 inch) tangs 1 dragon wrasse juv. (will eventually come out as he gets older), 1 red wrasse juv., 1 golden headed sleeper gobie, 1(1.5 inch porcupine puffer). I also have 5 brittle stars, 40 scarlet crabs 60 assorted snails, a pair of coral banded shrimp, 4 emerald crabs, 3 cucumbers and many other little inverates that escape me. Now for the question since this not actually a reef tank but more of a fancy FO. What should my salinity and temp be at ? Currently the tank is at 76 temp and 1.024 salinity any suggestions.

No offense intended, but my suggestion would be that you read Ron's excellent article at http// -- that ought to provide you with all the information you need to decide to increase both your temperature and salinity to something closer to those actually occurring on a natural reef.


Subject Re What's your salinity (corrected for temp)?

The definition of salinity is such that it does not change as a function of temperature.

so what the article is saying even though this is a modified reef I should keep my salinity closer to 1.026 - 1.028

That isn't a salinity value, it is a specific gravity value. Your hydrometer should have come with instructions on how to at least get a temperature-corrected specific gravity value, and it really ought to tell you how to convert that value into practical salinity units.

and my temp at about 80-82 ?

That seems like a reasonable target for most organisms. Actually I tend to target 80 F because I don't have really tight temperature control on the high side.

Ron has given the community a hypothesis regarding what conditions are "optimal" for most species of corals that we are likely to keep. At the center of this hypothesis is the assumption that the conditions in the region of peak coral diversity are optimal for coral growth. What people need to understand is that this is a hypothesis, and further, that Ron has exercised some judgement as to what parameters are most relevant. He picked temperature and salinity. It might also be that potential habitat space is highest in that part of the world, and that is what is most important.

As far as the salinity thing goes, I don't see any compelling reason for going to salinities lower than 35 PSU. If for no other reason, it cuts down on the number of questions I get about why people who run their system at low salinities discover that every time they get a new test kit (magnesium, calcium, etc) their systems are running at significantly lower than natural seawater values.

As far as the temperature issue is concerned, I don't think it was stressed adequately that there are very strong negative implications to running your system a few degrees higher than the band that Ron suggests. Although Ron seems to feel that temperatures around 90 usually aren't a problem, my experience is substantially different than that. Every time my system has made an excursion into the 90s, seriously bad shit has happened.

Organisms tend to grow faster even slightly past the point when response systems activated by excessively high temperatures start to be activated. And usually things go to hell in a handbasket really rapidly past that point. From a system husbandry perspective, I like to stand back from that line by several degrees. As I said, I don't have strong high-side temperature control in my system.

The other implicit assumption is that one is able to recreate the rest of the physical and chemical factors present in the ocean at the center of coral diversity. Our tanks tend to have sluggish water motion compared to that in the wild, they probably have higher than typical concentrations of biochemical warfare agents produced by the animals, etc. The water motion issue is probably one of the most critical factors in getting metabolites into and out of corals. I would suggest that it may be a good reason to stand off a little from the mid-80s for that reason alone. Because if water motion isn't great, the animals are just not going to be able to get things into and out of the boundary layer around them quickly enough.

I do agree with Ron that suggested temps in the mid-70s are too low. I agree with Ron that suggested salinities of 25 PSU (not specific gravity) are too low. I agree with Ron that a target salinity of 35 PSU is appropriate. I chose to target system temperature somewhat lower than he suggests for very well considered reasons.


I am sorry that I didn't have time to write a proper response yesterday, but fortunately Craig has already hit on most of the salient points anyway ;)

I agree with both Keith and Craig that you will probably want to throttle back a little on Ron's recommendations, but certainly want to go higher than what you are currently running. As I have said in previous discussions on this topic, I believe that you want to maintain your salinity (as Craig pointed out salinity is a measure of the solute content in water, and will not change with temperature - you're measuring the specific gravity -- a weight ratio -- as a proxy for salinity) at roughly 35-36 ppt (parts per thousand) and your temperature at the lower end around 80F and the upper end around 84F.

In addition to the points that Craig has made, I have 2 specific reasons for not wanting to maintain tank temperatures within the range that Ron points out are occurring on natural reefs today. First, there is pretty good evidence of an increase in the average water temperature of the world's oceans over the past century, and a best guess estimate runs somewhere in the range of 1-2C (plus or minus 1-2, BTW) that has led to a pretty dramatic shift documented in the species distributions of a variety of marine organisms. Couple that with the fact that surface seawater temperatures (SST) are used with very high accuracy to predict bleaching in reef corals around the world, and that the magic number for bleaching seems to be 1C above the long-term average for 2 consecutive months, or 2C above for 1 month, and that suggests that corals are living pretty close to their thermal maximum. In fact in the last major bleaching event, there were many reefs that remained above the long-term average for 5 consecutive months, and these reefs lost an average of 90% of the living corals due to factors associated with thermal stress. Second, given the tendency among hobbyists (and I include myself here) to lean towards drastic overstocking of our tanks relative to natural organism densities, maintaining a slightly depressed temperature means that the metabolic rate of the organisms in the aquarium is also slightly depressed, giving a little extra cushion in terms of supporting the bioload we generally maintain in our little glass boxes.

These two factors, I feel, provide an excellent reason to aim for maintaining aquarium temperatures closer to the long-term average temperature on the reef rather than the currently recorded maximum temperatures, i.e., roughly 82-84F depending on the site and so on. However I can see no good argument for maintaining a salinity lower than that found on natural reefs. As I said above, I didn't have time to really write an adequate reply yesterday, but I felt that Joseph should at least be exposed to a well-supported thesis on why to increase his tank temperature and salinity well above the standard recommendation found in most places. Craig is absolutely right that there is considerable debate on the factors determining the distribution and abundance of coral species in the world, but there is every reason to suspect that, regardless of the primary factors determining species ranges, physical factors (in particular temperature and salinity) play at least some significant role. Given that there is not a coral reef (in the true sense of the word) in the world found living in the water conditions recommended on the back of a bag of Instant Ocean (or whatever your favorite brand of salt happens to be), I feel it is important to warn people like Joseph that they should think carefully about where those recommendations come from and whether or not they make any sense...

After all that, to finally answer your question Joseph, try to aim for 1 point of SG or 1C of temperature a day as a reasonable rate of change for your aquarium. When increasing your salinity, you'll want to make sure that you know what your hydrometer is measuring and to what temperature it is calibrated so that you have a reasonable idea of your true salinity (aquarium hydrometers are notoriously inaccurate, BTW, and we tested a half dozen in a lab once and got reading of 1.027 to 1.020 on a sample of seawater that was 35 ppt at 20C). The easiest way to increase your salinity is to simply allow your tank to evaporate and make up evaporation with dilute saltwater rather than pure fresh. As for temperature, just aim for 1C per day, and it ought to be a very easy transition for your critters (natural reefs fluctuate by as much as 3-5C -- see DBW's temperature data on the GBR at http// for example).

Good luck with your tank.

Created by liquid
Last modified 2006-11-24 18:39