I have not updated in a while now so I thought I would again.
I was abroad for about six weeks in August up to mid-September, and left the tank alone. The water level dropped substantially during this time, and an algal bloom occurred. My dad topped it up a little thankfully to avoid it getting too bad, but I imagine there was still a pretty substantial hike in salinity (at least 40% of the water had evaporated). Also, the temperature has been dropping lately as summer is over. Because the tank is in an outdoor boiler room that is not strongly insulated (and the boiler turns off at times during the day), there is some fluctuation. I have shifted the aquarium heater up a few degrees to account for this.
This time, the algae was a dark, thick green slime I had not seen before. I looked into cyano on the internet and it does not smell like that. In addition, the snails do eat it unlike cyano, but it seems to grow at too fast a rate for them to clear. I think the drop in water level killed off some of the higher placed chaeto, and this sent nutrients shooting up again. Thankfully, both snails seem to have survived this experience, and most of the shrimp seem to be doing fine, although it is hard to keep count. I saw 5-6 swimming around in the visible part of the tank, but did not check the back where most of them hide. The cloudy water has cleared up substantially. I think the reason for the cloudy water was due to interference with the substrate (killing off bacteria through gravel vacuuming too extensively), so after being left undisturbed, it cleared up naturally. I did another gravel vac but a lot lighter and sucking up a lot less of the substrate, just to clear some of the algae and poop off the top of the substrate.
However, there is some red growth underneath the substrate (can see it through the glass) that could be cyano. I last checked the tank a week ago, and it seemed fairly fine then. I will check again in a few weeks time.