5 Good Reasons to Keep a Marine Aquarium Journal

It's helpful to document your aquarium because you won't remember everything

It’s helpful to document your aquarium because you won’t remember everything

Quick! What were your aquarium’s water parameters in the fourth week of January? When was the last time you performed a water change and exactly how much did you change? Can you recall precisely when you last swapped out your old light bulbs/tubes for a new set? How about your chemical-filter medium? When is it due to be replaced or replenished?

If, like Sheldon Cooper, you happen to have an eidetic memory, this type of information may be right there on the tip of your tongue, but for those with average powers of recollection (or, in my case, a lone functioning brain cell), such data isn’t always so easy to recall. That’s why keeping a marine aquarium journal can be so advantageous.

What you record in your aquarium journal (or logbook or diary or whatever you prefer to call it) is entirely up to you, but the more information you keep track of, the better. Here are some examples of potentially noteworthy data:

  • Water parameter test results
  • Timing and scope of water changes and other maintenance chores
  • Livestock additions/losses
  • The addition or upgrade of equipment
  • Unusual livestock behavior
  • Your feeding regimen or any changes to same
  • Dosing of supplements/additives
  • The quarantine protocols used for new specimens
  • Medications/treatments you’ve administered

What good might recording all this data do for you? Here are five potential benefits:

1) Catching drifting water parameters early

If you consistently record your water parameter test results in your journal and compare them to the previous set, you should be able to detect any shifts away from the desired ranges while they’re still relatively small, easy to rectify, and of minimal consequence to your livestock.

2) Staying on schedule with maintenance

If your mind works anything like mine does, you only think your last water change was two weeks ago and that you have another two months before you need to replace those metal halide bulbs. In actuality, you may be off by a long shot on both counts if you rely on memory alone. Drift too far off schedule with these basic chores, and it won’t be long before your livestock pays a price.

3) Getting to the root of problems

Many of the “unexpected” problems marine aquarists experience (algae outbreaks, livestock deaths, etc.) are actually more predictable than we’d like to believe—though more so in retrospect. It may just take a little sleuthing.

For example, if you “suddenly” develop an algae problem and look back through your aquarium journal, you may note a correlation between the outbreak and a rise in the nitrate and/or phosphate levels in your tank, or that the problem began shortly after the death of a herbivorous species that had been keeping the algae in check.

Or, if you observe that a fish specimen has begun to look thin and emaciated, a glance at your journal may reveal a correlation between the fish’s condition and a recent change in the foods you’ve been offering.

4) Having data to share with expert problem solvers

If you can’t get to the root of the problem on your own and it becomes necessary to query an expert (e.g., at your local fish store or online), he or she is certain to ask about your water parameters, what you’re feeding, any medications you’ve tried, all the livestock sharing the tank, the behavior of the livestock, what (if anything) you’ve changed recently, whether any new specimens were recently introduced, whether all new specimens are quarantined, and so on. The more detailed information you can provide, the easier it will be for the expert to help you identify the problem and advise you on the right solution.

5) Avoiding making the same mistakes twice

As they say, “Those who don’t learn from history are doomed to repeat it.” By learning to correlate aquarium problems with preceding trends or events (which should be evident if you carefully examine the data recorded in your journal), you should be able to avoid repeating those same mistakes in the future.

Photo credit: insEyedout

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About Jeff Kurtz

Jeff Kurtz is the Co-founder/Editor of Saltwater Smarts, former Senior Consulting Editor for Tropical Fish Hobbyist Magazine, and the aquarist formerly known as “The Salt Creep.” He has been an aquarium hobbyist for over 30 years and is an avid scuba diver.


  1. all great points in this article and solid advice. the journal is a great way to capture and keep all that information handy. it might be helpful to keep a list of the ‘stuff’ in your aquarium in the front of your journal too, in case there are any problems down the road caused by livestock.

    • Jeff Kurtz says:

      That’s a great point, Al. I always think I’ll remember all the livestock in my tank, but the minute someone asks me what I have and I’m not standing right in front of the tank, my mind goes blank and I leave something out.

  2. Paul Baldassano says:

    I still have many pages of my log from when I started my tank in 1971. It is interesting now to see how much I paid for a specimen and where I bought it. Very few of those stores are still in business. I also documented how long it lived which, in those days was not very long as tanks were fish only and we only used dead bleached corals. I listed any medications I used and if they did anything besides make the water a nice florescent color.
    I noted things like when I changed water and if I collected it and where.

    As I look at those notes I am amazed that this is the same hobby.

    • Jeff Kurtz says:

      Great insights as always, Paul! I can only imagine the challenges you must have faced back in those early days trying to keep livestock alive and thriving with so little information to guide you. And we think we have it tough now!

  3. Paul Baldassano says:

    Jeff, there was virtually no information in those days. No one carried salt water anything. Pumps, filters and lights were mostly made of metal and for fresh water. There were no powerheads, no salt water foods, no books or magazines, no substraits except fresh water gravel. (I used driveway gravel) of course no computers, no ASW, (I collected water in the East River next to Manhattan) no test kits. All glass tanks had just came out a few years earlier.

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