Routine Maintenance and Water Changes

A reef system changes every day: animals eat and grow, water evaporates, filters fill, media is used up, and equipment wears. Routine maintenance keeps those slow changes from adding up to a crisis. It's also how you learn what normal looks like for each system, so that anything different stands out (Module 1).

Look before you touch. Start every visit by looking: every animal, every piece of equipment, the water level, the floor. Something you change before looking can hide the evidence of a problem.

Same tasks, same order. A fixed routine means nothing is skipped on a busy day. Work one system at a time, with that system's own tools, so nothing is carried from one system to the next (Module 23).

Write it down. Every task, reading and change goes in the log: what was done, when, how much, and what the readings were. A log turns a vague feeling that something is off into a clear trend, and tells the next person what has already been done (Module 20).

Temperature. Read the temperature by hand with a meter in the water, on every system. Don't copy the number from a controller's display: if the controller or its probe fails, its number is wrong too (Modules 5 and 14).

Every animal. Find and look at every animal. Fish should be out and swimming normally, corals and clams open, anemones in their usual shape. Watch the animals at feeding: an animal that stops eating is often the first sign of a problem (Module 30).

Every part running. Check that pumps are running and flow looks normal, heaters and their controllers show normal readings, the skimmer is producing and its cup isn't close to full, and the top-off reservoir has water in it (Modules 13, 14, 16 and 20).

The water. Check water levels in the display and sump, look for leaks on the stand and the floor, and wipe away salt creep. Salt creep conducts electricity, so it's never left for later (Module 2).

If something isn't right, fix it if you can, report it if you can't, and write it in the log either way.

On a schedule. Filter socks are changed on set days, whether or not they look full (Module 15). Skimmers are taken apart and cleaned on a schedule (Module 16). Water is tested on the system's testing schedule (Module 7). Water changes follow their own schedule (section 8). The top-off reservoir is refilled with purified water before it runs low (Modules 4 and 20).

Less often. Activated carbon is replaced on a fixed schedule, because used-up carbon looks the same as fresh carbon (Module 17). Test tools are calibrated and verified on their schedule (Module 7). Pumps are taken apart and cleaned (Module 13), air stones are replaced (Module 16), and the RO/DI unit's stages are changed on their intervals (Module 4).

Keep a written schedule for each system that says which task is done on which day, and tick each task off in the log when it's done. A task that isn't written down is easy to forget, and nobody can tell afterward whether it happened.

Glass and surfaces. Clean the inside glass with a scraper or magnet cleaner, slowly near the silicone seams and the sand, and keep the outside glass, lids and stand clean. Wipe salt creep with fresh water, then wipe it dry so no white mark is left.

Keep the biology alive. Media and rock stay wet throughout maintenance: bacteria on media that dries out die (Module 8). Replace biological media in parts, never all on one day, so most of the bacteria stay in the system. Never siphon or vacuum a reef sand bed; its fauna keep it clean (Module 22).

Clean tools only. Use buckets, tubes and tools kept only for aquarium work. A bucket that once held soap, cleaning products or chemicals can put them straight into the water. Wash tools with hot water, and if they're sprayed with alcohol, leave them until they're completely dry before they touch tank water (Module 23).

A water change takes a measured amount of water out of a system and replaces it with new salt water made from purified water (Module 5). New salt water has no nitrate, phosphate, ammonia or waste in it, so a water change lowers all of them by the same share: a 10% water change takes out 10% of what's dissolved.

Water changes also take out things that are hard to test for, such as chemicals released by corals or a medication that has gone into the wrong system, and they help bring the water back toward normal after an imbalance (Modules 17 and 19).

The math sets the limits (Module 17). Four weekly 10% changes take out 34% over a month, roughly the same as one 40% change a month. A water change only dilutes: if something is still adding ammonia or nitrate, the level climbs again afterward. Doing the arithmetic for a real system is covered in Module 35.

Make the new water ahead of time in a separate container, following Module 5: purified water, heated to the system's temperature, salt added into the water, mixed until clear, then measured. Make enough for the change, plus a little extra in case something goes wrong.

Test the system before the change: salinity, alkalinity, nitrate and phosphate. The results tell you whether the routine change is enough, and the salinity and alkalinity tell you what the new water must match.

Match the new water. Measure the new water's salinity and temperature, and the system's. A difference of up to 1 ppt in salinity isn't a problem; don't chase an exact match. Temperature matters as much as salinity. For a large change made because something is wrong, match alkalinity as well (Module 8). Every batch is a new batch: measure it, even if last week's was fine.

Know the volume. Use buckets or containers marked with their volume, so the amount taken out and put back is measured, not guessed. Gather towels and keep a clear path to the drain.

1. Make it safe. Clean the glass first, so the debris comes out with the old water. Switch off the top-off, or it will refill the system with purified water as the level drops (Module 20). Unplug any heater that the falling water will leave in the air: heater glass can crack out of the water (Module 14). Switch off the return pump if the sump level will drop, so it doesn't suck in air or run dry (Module 12), and switch off the skimmer. Keep the temperature probe in the water. Dry your hands before touching any plug (Module 2).

2. Take water out. Siphon or pump the measured volume from the water column or the sump into marked buckets. Never siphon the sand. Replace filter socks if they're due.

3. Add new water. Check the new water's salinity and temperature once more, then add it slowly with a pump and tubing. Don't walk away while it's filling: an unwatched fill overflows.

4. Restore in order. When the water is back to its normal level, switch the return pump on, plug the heaters back in once they're fully under water, switch the skimmer on, and switch the top-off on last, once the level is at its normal line.

5. Check and log. Check the temperature by hand, the flow, the skimmer, the water level and the floor. Wipe up spills and salt creep, watch the animals for a few minutes, and log the volume, the new water's salinity and temperature, and the system readings.

Routine changes. A common routine is 10% to 15% of the total water volume every 1 to 2 weeks. A 10% change every week and a 20% change every other week give a similar result. The percentage is of the system's real water volume, display and sump together, after rock and sand take their share (Module 36).

Large changes. The larger the change, the further the system's water moves toward the new water. Changes over 20% are done only with new water that's heated and closely matched to the system, or they can shock the animals with a sudden change in temperature or chemistry.

Follow the system's schedule. Each system has its own water change schedule, set from its size, stocking and test results. Keep to it, record every change, and don't skip one because the water looks clear: clear water says nothing about what's dissolved in it.

This course's rule: when in doubt, do a matched water change. Matched means the new water's temperature and salinity match the system's, and its alkalinity too when the change is large.

If ammonia or nitrite is above zero, a matched water change lowers it at once and protects the animals while you look for the cause, such as something dead, a clog or overfeeding (Module 8). If something has gotten into the water, such as a medication, a spill, or chemicals released by a coral, water changes and fresh activated carbon take it out (Module 17). If animals are unsettled and the cause isn't known, a water change buys time without making things worse.

It buys time; it isn't the fix. Keep looking for the cause while you do it. If the level comes back two days later, the cause is still there.

Unmatched or untested new water. New water that's colder, warmer or far off in salinity gives the animals a second problem on top of the first. Match it first, or don't do the change.

The new water is the problem. If the purified water's TDS reading is above zero (Module 4), or the salt batch is off, a water change puts more of the problem in. Fix the source water first.

Nutrients already at zero. In a system with nitrate and phosphate at zero, for example one fighting dinoflagellates, extra water changes strip the nutrients further and make it worse (Module 31).

An equipment fault. A failed pump, a heater stuck on or a top-off stuck open is fixed at the equipment. A water change doesn't touch the cause, and it can hide it for a while.

A treatment container. In a hospital container, a water change also removes medication, so the new water is dosed to keep the treatment level (Module 30).