Daily Maintenance, 5 Minutes

Daily maintenance isn’t about doing work, it’s about observing. A five-minute
visual inspection every day is your earliest warning system. Problems that get
caught at day one are almost always fixable. Problems that get caught at day ten
are often not.

Visual Check of All Livestock

Look at every fish and every coral. This doesn’t require stopping what you’re
doing, a 60-second scan while the lights are on is enough. You’re looking for:

• Fish: Any fish that isn’t visible at its usual time of day. Any fish showing clamped fins, rapid breathing, white spots, or unusual swimming behavior. Any fish hiding that doesn’t normally hide.
• Corals: Any coral that was open yesterday and is closed today. Color changes, a coral going from bright to pale or browning is a slower signal, but a coral that closes suddenly is an immediate one. Any coral that appears to be receding, shrinking, or developing tissue loss.
• Tank surface: Any unusual film, foam, or oily sheen on the water surface suggests a skimmer issue or elevated organics.

The value of the daily check is baseline familiarity. You need to know what
“normal” looks like for every inhabitant in your specific tank in order to
recognize when something has changed. This is impossible to develop from
weekly observations alone.

Top Off Evaporated Water

Reef tanks lose water to evaporation continuously, typically 0.5–2% of total
volume per day depending on tank size, surface agitation, temperature, and room
humidity. As pure water evaporates, salt stays behind. Salinity rises. In a
20-gallon tank losing half a gallon per day, salinity can climb from 1.025 to
1.028 in under two weeks without top-offs.

Top off with RODI water only, never saltwater. The goal is to replace the
pure water that left, not add more salt. Add the top-off slowly, into a high-flow
area of the tank to mix it immediately rather than dropping cold, low-salinity
water directly onto corals.

The better solution: an Auto Top Off (ATO) unit. An ATO uses
a float switch or optical sensor to detect the water level dropping and
automatically doses RODI water to compensate. It removes the most common source
of salinity variance from beginner tanks entirely, the days you forgot to top off.
See: Best Auto Top Off Systems

Check Equipment Is Running

A 10-second confirmation that the return pump is circulating, the wavemaker is
producing flow, and the heater light is on. Equipment failures are usually
obvious, the tank goes silent, flow stops, or temperature drops, but a quick
daily check catches the less obvious partial failures: a pump running at reduced
speed, a heater clicking on and off more frequently than normal, a wavemaker
that’s stopped pulsing and is running on constant mode.

Weekly Maintenance, 15–20 Minutes

Test Parameters and Log Results

The weekly parameter test is the most important maintenance task in the entire
routine. Every other task supports the goal of stable parameters, this is
how you verify whether you’re achieving it.

What to test weekly:

• Alkalinity (dKH), target 8–10 dKH, stable week to week.
  This is the most important parameter to track consistently once corals are
  in the tank. A drop of more than 0.5 dKH week over week signals that demand
  is outpacing supply, either more corals consuming it, or a dosing shortfall.
  Test with Salifert or a Hanna HI755 checker for the most reliable results.
• Salinity, target 1.025–1.026 specific gravity. Test with
  a refractometer. If salinity is reading high, top-off water is falling behind
  evaporation. If reading low, too much fresh water has been added.
• Nitrate (NO₃), target under 10 ppm for a reef with corals.
  A rising nitrate trend week over week is a signal that nutrient export
  (water changes, skimmer, refugium) is falling behind nutrient input (feeding,
  bioload). Don’t chase a single reading, watch the trend.
• Temperature, confirm with an independent thermometer,
  not the heater dial. Record the reading. Temperature variance within a week
  (e.g. day vs. night swing greater than 2°F) is worth investigating.

Add these when corals are established:

• Calcium (Ca), target 400–450 ppm. Tracks alongside alkalinity consumption by stony corals.
• Magnesium (Mg), target 1250–1350 ppm. Test monthly is sufficient in a stable tank; add to weekly testing if alkalinity or calcium are hard to stabilize.
• Phosphate (PO₄), target under 0.05 ppm in a reef. Use a Hanna HI736 ULR checker for accurate results at reef-relevant concentrations.

Write every result in a log, date, time, and value for every parameter tested.
The log is your most valuable diagnostic tool. When something goes wrong,
the first question is always “when did this start?”, and the log answers it.
A spreadsheet with date columns and one row per parameter takes three minutes
to update weekly and is worth months of detective work when you need it.

See: Reef Tank Water Testing Guide |
Best Reef Tank Test Kits for Beginners

Clean the Glass

Coralline algae and green film algae accumulate on the front and side glass
of an established reef tank weekly. A magnetic glass cleaner handles this in
under two minutes, run it across the interior glass surface before the water
change so that dislodged algae gets removed during the siphon.

A few practical notes:

• Clean the front glass first, then sides. Don’t skip the corners, algae accumulates there and is harder to remove once it’s established.
• If the magnetic cleaner loses grip and drops to the sandbed, retrieve it carefully, sand trapped between the magnet and the glass will scratch acrylic tanks permanently.
• For acrylic tanks, use a cleaner rated for acrylic specifically, standard glass cleaners will scratch.
• Coralline algae on the back glass can be left to grow, it signals good water chemistry and provides a natural-looking background.

Check and Empty the Skimmer Cup

The protein skimmer collection cup accumulates dark, protein-rich skimmate.
In a reef tank with active feeding and a meaningful bioload, this fills in
5–10 days. Check it weekly and empty before it reaches the overflow point, a cup that overflows sends skimmate back into the water column, negating the
purpose of the skimmer entirely.

When emptying: remove the cup, dispose of the skimmate (it’s excellent garden
fertilizer), and wipe the cup neck clean with a damp cloth. Salt creep on the
neck reduces the contact surface for foam and degrades skimming efficiency over
time. A clean cup each week takes 30 seconds.

While the skimmer cup is out, look at the skimmate color and consistency, it tells you something about tank conditions:

• Dark, thick, dry skimmate: Skimmer is dialed in well. Normal output.
• Thin, light tan, watery overflow: Skimmer is running too wet. Raise the water level in the skimmer body slightly. Also common immediately after a water change or when new coral or food is introduced.
• No output for 2+ weeks: Skimmer may be underperforming, water level too high, or organic load too low. Check output valve/gate setting and pump flow.

Verify Flow and Temperature

Confirm the wavemaker is producing the expected flow pattern, powerheads can
slow down as impellers collect biofilm and salt creep. Verify the temperature
reads within 1°F of your target. Check for any changes in equipment noise, a pump developing a rattle or grinding sound is a warning before failure, not
after.

Bi-Weekly Maintenance, 30–45 Minutes

Water Change, 10–15% of Tank Volume

The water change is the single most effective routine maintenance action you
can take. It accomplishes three things simultaneously that no piece of equipment
can fully replicate:

1. Removes accumulated nitrate and phosphate that biological filtration and skimming can’t fully export
2. Replenishes trace elements, iodine, strontium, zinc, and dozens of other compounds that corals consume and that aren’t present in top-off water or replacement dosing
3. Dilutes dissolved organics that accumulate over time and contribute to the yellow tinting (yellowing) of water that reduces light penetration to corals

For most beginner reef tanks, a 10–15% water change every two weeks is the
standard routine. Some reefers prefer 10% weekly, either approach works.
What doesn’t work is 30% monthly, large infrequent changes produce the
parameter swings that smaller more frequent changes prevent.

How to Do the Water Change Correctly

1. Mix saltwater in advance. Mix RODI water with reef-grade salt
   to 1.025–1.026 specific gravity at least 24 hours before the water change.
   Use a powerhead or airstone to mix and aerate thoroughly. Verify salinity with
   a refractometer before using.
2. Match temperature. The replacement water should be within
   1–2°F of the tank temperature before it goes in. Cold water change water
   is one of the most common causes of immediate coral stress, corals close,
   fish flash, and the tank takes hours to restabilize.
3. Remove water first. Use a siphon tube to remove 10–15% of
   tank volume. Direct the siphon to the sandbed during removal and siphon up
   detritus from the sand surface and from behind and beneath the rockwork.
   Accumulated detritus is a continuous source of nitrate and phosphate, removing
   it during the water change is more effective than any additive.
4. Add new water slowly. Pour replacement water in slowly, ideally over 5–10 minutes, or use a pump with a low output rate. Dumping
   replacement water in quickly disrupts the sandbed, stresses corals, and can
   cause localized salinity and temperature swings.
5. Verify salinity afterward. Test salinity 15–20 minutes after
   the water change, once the tank has mixed fully. It should read within
   0.001 of your target. Adjust future batches if consistent drift is observed.

See: How to Do Water Changes in a Reef Tank

Replace Filter Floss

Filter floss (mechanical filter media in the rear chambers of AIO tanks) traps
particulate matter, uneaten food, detritus, coral mucus. This is its job.
The problem is that trapped organic material immediately begins decomposing
and releasing nitrate and phosphate back into the water. Filter floss that
isn’t changed frequently becomes a net negative, it’s adding nutrients faster
than it’s removing them.

Change filter floss every 5–7 days in a fed reef tank. At minimum, every bi-weekly
water change. Never rinse and reuse, the decomposing material is bonded to the
floss and doesn’t rinse out effectively. Replacement filter floss is inexpensive;
the nitrate contribution of used floss is not worth the savings.

Siphon Detritus

During the water change siphon, systematically move the tube across the full
surface of the sandbed, not just the visible areas, but behind and beneath
the rockwork where flow is lowest and detritus accumulates fastest. Also check
the rear filtration chambers of AIO tanks, detritus settles in corners of
chambers where flow is minimal and can become significant nutrient sources
if left for weeks.

Don’t aggressively vacuum the deep sandbed, disturbing the full depth of the
sand releases hydrogen sulfide from anaerobic zones and can crash parameters
rapidly. Work only the top 0.5 inches during routine maintenance.

Monthly Maintenance, 30–45 Minutes

Clean Pump Impellers

Return pumps and wavemaker impellers accumulate biofilm, coralline algae,
and salt creep that gradually reduces flow output. A pump running at 70% of
its rated flow from impeller fouling is a common and invisible cause of
declining water quality and dead spots in the tank.

Monthly impeller cleaning:

1. Unplug the pump
2. Remove the impeller housing, usually a quarter-turn or clip mechanism
3. Remove the impeller and rinse under RODI water (not tap, minerals in tap water can damage some impeller materials)
4. Use a small brush (a dedicated pump cleaning brush or a toothbrush) to remove biofilm from the impeller blades and housing interior
5. Reassemble and confirm the pump is running at normal flow before leaving

Do not clean return pump and wavemaker on the same day if possible, cleaning
both simultaneously removes a significant portion of the beneficial bacteria
that has colonized the pump surfaces. Stagger them by one week.

Replace Activated Carbon

Activated carbon removes dissolved organics, terpenes from leather corals,
medications residue, and the compounds that cause water yellowing. It exhausts
after 3–4 weeks of use, carbon that’s been running for two months is doing
nothing useful and taking up media chamber space.

Replace with fresh activated carbon monthly. Use a media bag rated for
aquarium use, loose carbon in the chamber can leach dust into the water column.
Rinse the new carbon under RODI water before placing to remove carbon dust.

Full Parameter Test

The monthly test expands beyond the weekly routine to cover every parameter
relevant to your tank’s inhabitants:

• Alkalinity, calcium, magnesium
• Nitrate, phosphate
• Salinity, temperature, pH
• Ammonia and nitrite (should read 0, if they don’t, something is wrong with biological filtration)

The monthly full test gives you a comprehensive snapshot that the weekly
abbreviated test doesn’t provide. Compare it to the previous month’s full test, the 30-day trend is more informative than any single weekly reading.

Inspect All Equipment

A monthly equipment inspection takes 10 minutes and catches failures before
they become losses:

• Heater: Verify temperature against an independent thermometer. Check for cracks or discoloration on the glass body.
• Return pump: Confirm flow rate feels consistent with previous months. Check tubing for kinks or salt creep blocking flow.
• Wavemaker: Confirm suction cups are holding and the pump head is positioned correctly. Verify wave modes are functioning as set.
• Skimmer: Check all seals and o-rings for wear. Confirm the gate valve or output pipe moves freely without sticking.
• Lighting: Verify the schedule is running correctly on the timer or controller. Check that all LEDs are functioning, a dead LED cluster is not always obvious under the full fixture running.
• ATO (if present): Confirm the float switch or sensor is triggering correctly. Verify the RODI reservoir level is adequate.

Quarterly Maintenance, 30–60 Minutes

Deep Clean the Skimmer Body

The skimmer neck, bubble plate, and internal walls accumulate salt creep and
biofilm that the weekly cup cleaning doesn’t address. A quarterly skimmer
teardown, full disassembly, soak in a vinegar/water solution for 30–60 minutes,
rinse thoroughly with RODI water, and reassemble, restores performance and
extends the skimmer’s lifespan meaningfully.

Allow 24–48 hours of break-in after a deep clean before judging skimmate output, a freshly cleaned skimmer often runs wet or produces little output until
the surfaces re-establish a biological film.

Calibrate the Heater

Heater thermostats drift over time. Quarterly calibration, checking the
heater’s dial setting against the actual tank temperature measured by an
independent calibrated thermometer, catches drift before it becomes a problem.
The Eheim Jager has a recalibration dial built in for this purpose. Other
heaters require adjustment of the temperature dial to compensate for any
measured offset.

See: Best Reef Tank Heaters for Beginners

Review the Lighting Schedule

Quarterly is a good time to evaluate whether your lighting schedule matches
your tank’s current needs. A tank that started with soft corals and has
added LPS may benefit from slightly higher intensity at the midday peak.
A tank where coral bleaching has occurred needs intensity reduced.

Also check whether the lighting timer or controller has experienced any drift, some controllers lose time gradually and end up running the light cycle off-schedule
from the actual clock, which can disrupt coral behavior if the difference becomes significant.

Inspect Rockwork and Aquascape Stability

Over months, corals grow, fish rearrange rubble, and rockwork can shift slightly.
A quarterly inspection of aquascape stability, confirming no key rocks have
shifted, no structures are at risk of toppling, no coral colonies have grown
into contact with neighboring species, prevents the acute losses that come
from a rockfall or an unnoticed coral war that’s been progressing for weeks.