I will do the water test when I get back home. We only had a digital one in there before and it was reading 75.6. The water felt very warm so I turned off the heaters and my wife went to get an non digital thermometer. A few hours later when she put in the analog thermometer in, the digital one was reading 66.6 and the analog was reading 81 or so. Imgur I wonder if that had something to do with it
I have never witnessed an analog thermometer misreading. If the water feels warm to the touch, it's in the 80s, not 60s. Please do not just turn your heater off though, consistent temperatures are more important than anything. If it is too high you can lower it slowly. What lives in the tank? I assume they are tropical fish that need heat, so 60s is too low.
It is my understanding that warmer water contains less oxygen, so maybe that is the issue? I too would go with the analog over the digital thermometer- so your tank is super warm! I might unplug your heater (the tank will cool slowly enough) and test it in a bucket of water. I assume the heater is not set for 88 degrees - so has it broken? Put the heater in a bucket, set it, then in a couple of hours use the analog thermometer to check the temperature.
If the water feels warm, don't change temp. Constiancy is good. Higher temps mean that the water has less diffused oxygen in the water. You can help this with an airstone. Also, you said you had really bad algae, right? I've heard of this happening in ponds and such, sometimes in fish tanks, where there is an algae bloom. Eventually, the algae and microorganisms die and the decomposition process uses up the oxygen. This is called eutrophication, I believe.