Yeah, I know the discussion on controlling hair algae was rather lengthy but there are so many factors that can contribute to problems with nuisance algae, and nitrate can enter your aquarium in so many sneaky ways, that you never know which of those factors is contributing to the problem in any given case. I know that the vast majority of those factors don’t apply to your aquarium, Sandy, but I always feel obliged to run through the whole list anyway since you never can tell which of the suggestions for controlling nuisance algae may be most helpful for a particular hobbyist.
In your case, if you’re macroalgae is starting to take hold and outcompete most of the hair algae now, you might try using a small powerhead (with the intake well shielded and screened off, of course) in your tank positioned so that it will create brisk water movement in the corner where the remaining stubborn hair algae is still growing. Restoring good circulation and oxygenation to that spot may help tip the scales in favor of your macros or coralline algae rather than the hair algae.
I completely agree regarding your lighting — if your bulbs are only three months old, then a change in their output is unlikely to be contributing to the growth of hair algae.
Yes, I think you’re right about the elevated water temperatures, too, Sandy. A temperature spike above 80°F may well have triggered the pipefishes’ problem with fin rot. Getting the water temperatures back down in the comfort zone of your pipefishes and seahorses should help limit the bacterial growth and make it easier to resolve the fin rot.
In addition to lowering the temperature, you might also consider reducing the specific gravity of your tank during the treatment period since high-salinity sometimes contributes to fin rot, as discussed below in the following excerpt from my old Step-By-Step Book about Seahorses:
Fin Rot in Seahorses
"Fin rot is another problem that sometimes afflicts seahorses in captivity. When this happens, the alert aquarist will notice that the fins of the seahorse are beginning to look frayed and ragged for no apparent reason. This damage is most obvious in the dorsal fin, which is almost always the first to be attacked. In its early stages, this disease is evident as a fine white line along the edge of the fin, which gradually advances towards the base of the fin until the fin rays become exposed, protruding like the ribs of a tattered umbrella. If the bacterial rot is left untreated, the entire fin will be destroyed and the body tissues of the seahorse will become infected, at which point it can no longer be saved. Early detection and treatment is crucial for curing fin rot. At the first sign of fin rot, Mildred Bellamy recommends submerging the infected seahorse in a numeral 1:4000 solution of copper sulfate for one to two minutes. As she cautions, fishes undergoing this chemical baths should be watched closely and removed at the slightest sign of distress regardless of how much time has elapsed. A second bath should be administered in exactly the same manner 24 hours later. Along with these chemical dips, she also recommends that the infected fins be like a slob with a good bacteriocidal agent, such as hydrogen peroxide or merbromin (brand name Betadine), three or four times daily for a period of five to seven days. It may also be helpful to gradually lower the specific gravity of the aquarium water to about 1.020 during treatment, since fin rot is sometimes associated with high salinity.
"Providing the fin rot is detected early, or is only a mild infection, seahorses usually recover completely following this regimen of treatment, and the damage since will be fully regenerated. Once again, I must stress the fact that the key to recovery is stopping fin rot in its tracks before the bacteria penetrates the tissue and the body of the seahorse becomes infected."
Yes, it would be a good idea to darken the aquarium anytime you are treating it with nitrofurazone antibiotics such as the active ingredients in Furan2.
Best of luck resolving your pipefishes’ problem with fin rot, Sandy! If you can curb the infection, their fins will rapidly regenerate.