Yes, temperature fluctuations between 74 F and 75.5 F (23,2°C to 24,2°C) over the course of the day are perfectly acceptable, in my experience.
If you are keeping tropical seahorse is such as Hippocampus kuda, Hippocampus reidi, or Hippocampus comes, or a species with an exceptionally large range which can adapt to an equally large range of temperatures, such as Hippocampus erectus, then a maximum water temperature of 75.5° F should not cause an increase in disease problems.
However, always bear in mind the following information:
In general, as a rule, all seahorses do better at the lower end of their acceptable temperature range then at the upper end of their comfort zone, particularly in the small, closed system aquariums of the home hobbyist.
As you know, heat stress is extremely debilitating for seahorses and, in my experience, it is associated with more disease problems and mortalities in the home aquarium than any other factor. There are number of reasons for this. For one thing, elevated temperatures can have a very detrimental effect on the immune system of fishes. This is because many of the enzymes and proteins involved in their immune response are extremely temperature sensitive (Olin Feuerbacher, pers. com.). Some of these protective enzymes can be denatured and inactivated by an increase of just a few degrees in water temperature (Olin Feuerbacher, pers. com.). So when seahorses are kept at temperatures above their comfort zone, their immune system is compromised and they are unable to fend off diseases they would normally shrug off.
At the same time heat stress is weakening the seahorse’s immune response, the elevated temperatures are increasing the growth rate of microbes and making disease organisms all the more deadly. Research indicates that temperature plays a major role in the regulation of virulence genes (Olin Feuerbacher, pers. com.). As the temperature increases, virulence genes are switched on, so microorganisms that are completely harmless at cooler temperatures suddenly become pathogenic once the water warms up past a certain point. Thus both the population and virulence of the pathogens are dramatically increased at higher temperatures (Olin Feuerbacher, pers. com.).
If you have not already done so, Muffin, there is a simple technique that you can use to drop the water temperature in an aquarium by at least 3°F-5°F without the use of a chiller: either remove the cover or hood altogether, if possible, or at least keep the cover tilted open as far as possible. When the aquarium is tightly sealed, heat is trapped underneath the cover and the water temperature rises as a result. Removing the cover or hood, or at least cracking it open as much as possible, allows the trapped heat to escape and equalize with the ambient air temperature. It also reduces the humidity, which results in more efficient gas exchange at the air/water interface; the dissolved exigent levels are increased and the carbon dioxide levels are reduced as a result, which, in turn, helps to stabilize the aquarium pH in the proper range. If possible, you can simply remove the cover or hood altogether since there is no danger that your seahorses will jump out of the tank. If not, you may have to settle for lifting the lid part way the way you would when accessing the tank to feed the fishes, or by cracking it open.
You will find that the water temperature drops by several degrees if you can remove the cover or aquarium hood altogether, and it should drop at least 2°F-3°F even if you could only cracked the lid open. For example, this is what Ambrose, a seahorse keeper with a JBJ nano tank, reports in that regard:
“… my tank set up is a JBJ nano cube. I believe that it’s 20 in long, by 20 inch wide, and is 18 inches deep. It’s a closed top system that runs a 150 watt metal halide bulb. Heat with this tank has been an issue almost the whole time with this tank. And on the hottest days on the year the tank has seen temp as high as 82-83 degrees. I’ve found that leaving the tank lid cracked open has drastically reduced the tanks temp by 3-4 degrees. So that’s the way I’ve been leaving it lately (open top),the tank now stays at a steady 78-79 degrees constantly. That’s another trick that I only recently discovered…”
Notice that Ambrose was only able to leave the aquarium lid cracked open, but even so was able to lower the water temperature by around 4°F. That’s something that might be worth a try with your seahorse setup, Muffin.
The only drawback to this technique is that it increases the rate of evaporation so that you need to top off the tank with freshwater more frequently, but that’s merely a minor inconvenience.
One simple way to drop the water temp in your aquarium is to position a small fan so it blows across the surface of the water continually. This will lower the water temperature several degrees through the phenomenon of evaporative cooling. Most hobbyists find that small, clip-on fans that are equipped with a cord and all ready to go right off the shelf are the most convenient when they need to cool down one of my tanks, as Leslie Leddo described below:
Fans work great for decreasing tank temps. Small 6 to 8 inch plastic electric clip on fans are available at most home improvement centers and places like Longs or Rite Aide. They can be clipped on to the tank rim and adjusted so that the air from the fan blows across the surface of the water rippling it a bit. This works very well. I would suggest 2, one on either side of the tank.
It does increase evaporation quite a bit so you will need to top off more frequently.
However, if you try this technique, I must also caution you to observe all the usual precautions to prevent shocks and electrical accident when you are using an electric fan or any other electrical equipment on your aquarium, Muffin.
One such precaution is to install an inexpensive titanium grounding probe in your aquariums. That will protect your seahorses and other wet pets from stray voltage and should also safeguard them from electrocution in the event of a catastrophic heater failure or similar accident..
But the best way to protect you and your loved ones from electrical accidents around the fish room is to make sure all the outlets are equipped with Ground Fault Circuit Interrupters. And it’s a good idea to make sure all your electrical equipment is plugged into a surge protector as well to further protect your expensive pumps, filters, heaters, etc. from damage. Some good surge protectors, such as the Shock Busters, come with a GFCI built right into them so you can kill two birds with one stone. So when you set up your cooling fan(s) on the aquarium, be sure they’re plugged into a grounded outlet with a GFCI or a surge protector with GFCI protection.
Best of luck holding your seahorse system at the optimal temperature as economically as possible, Muffin.
Pete Giwojna, Ocean Rider Tech Support