My API master test kit does not test for the GH or KH, I have test strips for this though (I know not as accurate but only thing I have at the moment). Both the KH and GH are showing up at 50 on the test strips.
That's accurate enough for our purposes which is only to ascertain the relative softness/hardness of your water. I would assume these numbers are in ppm, so 50 ppm is very soft water (equivalent dGH is 3 dGH rounding it up). This explains the pH lowering. As organics accumulate, they are broken down by bacteria. This produces CO2 which in turn produces carbonic acid so the water pH lowers or becomes more acidic. That is not a problem for most soft water fish so it is nothing to worry aboout, but you need to understand it will occur and just let it do what it wants. Do not try to raise it with additives. Your only fish that will have difficulty in this are the guppies; livebearers (guppies, Endlers, platies, millies and swordtails to name the most common) must have much harder water to function properly, so the softness here will slowly weaken such fish. Don't acquire any more livebearers; re-home the guppies if you want, that's your call.
The above has nothing to do with the ram issue, but it was mentioned so now it has been explained.
I am sure that I have one male and one female, the “female” has a very pink belly area and the other does not. Up until about 3 days ago they were fine together. Swimming round and also resting next to each other. If one ever got too far away from the other they would appear to almost search for each other until reunited side by side.
From this info I would also assume a male/female, but likely they did not bond. Putting any female in with any male will only be successful if the two accept each other and bond. You need to observe them very closely; sit in front of the tank without moving for 20-30 minutes, so they "forget" you are there and will be inclined to act normally, not expecting food or something from you. If you see the male poking, head bunting, or chasing the female, then they are not bonding. This may be the case even if they do not show such behaviours. I went through this with a "pair" of Bolivian Rams several years ago; they spawned four times but always with what I now realize were behaviours indicating they were not bonding but putting up with each other, and overnight the male killed the female.
As for what to do, you should separate them and return one (the female would be my choice to re-home) if you can.
Water temperature is set at a stable 26 degrees, would my other fish be ok if I was to up the temp by 1 degree?
The danios are already having difficulty with this high (26C) a temp, it should be closer to 23 or 24C for danios as they are active swimmers [Are these Zebra Danios, or another species?]. Rasbora should be OK, depending upon species. I would leave the temp at 26C for now.
Temperature is crucial for fish, because it drives their metabolism. Each species is designed by nature/evolution to function best in very specific water parameters, and the more outside this range they are kept the harder they have to work just to maintain normal daily body functions, and it wears them down and weakens them over time.
I treated the tank with love fish white spot and parasite treatment.
I do not know anything about this, but in future I would just use heat (30C) for two weeks. All medications do affect fish detrimentally, even if they are really needed, so the simplest treatment is usually safer. This too is not likely the ram issue, though it could be a factor.