You mention that proper husbandry being as important as the temperature and I agree to a point. However, there are just SO many interpretations of "proper husbandry" that a new keeper can be in trouble before they realize that they aren't doing enough to keep the bacteria in check.
Looks like proper husbandry is exactly what we are discussing. Proper temperature is an aspect of proper husbandry. We are in some disagreement what is a proper and realistic temperature range. Your upper ceiling is close to my mid-range recommendation.
However, no matter how cool a tank is kept, temperature won't compensate for deficiencies in other aspects of proper care. BTW, some pathogenic bacteria flourish at cooler temperatures, it all depends on what environment they are adapted to.
I understand your points, but I think you are being a bit dogmatic. And why would you question that it can be difficult to maintain a temperature of 74 or LESS consistently without a chiller? Don't you have summer in Canada? I have a 1/3 hp chiller on my 210 gallon tank, which is lit by (cooler) PC fluorescents, and has low-heat water pumps. Even with the chiller set, and only two of the six lights going, the tank is difficult to maintain at below 77 F. This is not a seahorse tank, the example is to illustrate that it is not easy to keep tanks in the low 70s.
What I have seen is that many new keepers of seahorses have never kept a saltwater tank before. (Not the case with the OP.) I believe that failure with seahorses is not always due to temperature, but from not understanding proper maintenance of water quality. I'm not saying keeping lower temperatures is not one useful husbandry practice, but it doesn't replace other good practices, and it is not realistic to impose temperature conditions that are not necessary to seahorse health (68 or 69F for tropical species) that people may not be able to maintain.
For truly
subtropical and temperate seahorses, temperatures in the low 70s and considerably below (for temperate species) are appropriate at all times. For example, H. capensis should not be kept as a tropical seahorse. For tropical animals, I agree that mid-70s is the target temperature of where they should be kept. I think keeping the temperatures below 80 is a realistic ceiling for most keepers, and with proper husbandry, healthy animals will thrive in this range. I'm not saying 80 is good, I'm saying do what you can to stay a few degrees back from that ceiling. To say seahorses will die if you don't keep them at 74 all the time is not only wrong, it's unrealistic to expect without a chiller.
I agree on the need to update any current works on seahorses. I don't claim to be an expert, but I am an experienced hobbyist, experienced with seahorses, and I do know what I am talking about.
BTW, if you look on the seahorsesource site, the temperature range for tropical seahorses is consistent with what I would recommend, which is 72-77. Average of mid-70s, , +/- 2 or 3 degrees, being sure to keep it below 80. NOT 74 as the top limit.
You and I have each repeated/clarified our positions at least twice. How about we agree to disagree, even though I'm not sure we disagree all that much on proper care of seahorses?