I keep of record of significant changes/events to my tanks. I just have a page in a folder on my PC, one for each tank. I record the date the tank was set up with the substrate material, light tubes/bulbs data, and if it is a biotope the locale.
Any changes along the way are recorded, for example if I changed out the substrate, when I replace the light tubes/bulbs, if the "theme" changes, etc. Fluorescent tubes must be replaced regularly long before they actually burn out and 12 months (for my T8 tubes) is as long as they should go, so it is very useful knowing when I last changed them on this or that tank. I also record the date I put in new Flourish Tabs because these are every 3 months and I will never remember that long without records. When I had larger tanks with canister filters, the date the filter was cleaned was recorded, again because I will usually fail to remember after a few months.
I have never recorded daily temperature (it never varies anyway) nor feeding as that is so routine; I alternate three upper and three lower prepared foods, with a missed day usually Thursday sometimes Friday, and the frozen "treats" on Sunday a couple hours after the water changes. Easy to remember this.
I did test for pH and nitrate, immediately prior to the weekly water changes, and in a paper notebook as it was easier doing the tests on 8+ tanks and getting wet. I did this for a few years, though not every week after several weeks, and as the results were identical for well over five years...I stopped. Tanks do (or should) become stable biologically, and absolutely nothing is going to change this unless the aquarist meddles in them. The substantial water changes weekly, not overcrowding, not overfeeding, the right mix of species, proper water parameters (natural, no "adjusting" as this is where trouble enters) and proper aquascaping for the species...once you have this down, the tank should remain stable.
Got to move out of my 3rd floor flat.....
