Temperature Management

Lights, pumps, heaters and a warm room add heat. Evaporation, a cooler room, fans and chillers take it away. The water slowly follows the room around it (Module 5), so the room matters most.

This course's livable range is 26 to 30 C (Module 5). Inside it, a steady temperature matters more than any one number. This module covers the equipment that holds it there, how that equipment fails, and how to fix it.

A glass heater is a heating element in a glass tube, usually with a thermostat built in and a dial to set it. Glass can crack if it's knocked, or if it runs out of the water.

A titanium heater is a heating element in a titanium tube. It's much tougher than glass, but it usually has no thermostat of its own: it must be run from a separate controller, never plugged straight in. An inline heater sits in the plumbing and heats the water flowing through it.

Check that every heater is rated for salt water. Some heaters are sold for fresh water only. Titanium is on the IMARCS material list.

The rule of thumb is about 3 to 5 watts per gallon, which is about 0.8 to 1.3 W per liter. Use more when the room is cold or the target is far above room temperature.

For tanks over about 40 to 50 gallons (about 150 to 190 L), use two smaller heaters that together give the total, instead of one large one (section 7). Count the whole system volume: display, sump and plumbing (Module 36).

Put heaters where the flow is strong, such as near the return or in the sump, so warm water spreads evenly. Keep the heater under water at least to its minimum water line. Nothing, such as rock, sand or equipment, should touch a glass heater; uneven heating can weaken the tube.

Always unplug a heater before putting it in or taking it out of the water, and let it cool for at least 30 minutes before lifting it out. Check the glass for cracks before installing it. Every cord gets a drip loop (Module 2).

The pump chamber is the level that moves (Module 12). A heater placed there must stay under its line even when the level is low.

A typical controller has one probe and separate outlets for heating and cooling. Each outlet has its own set point. Between them is a dead band where neither runs, so the heater and chiller never fight. Don't set the switching gap (hysteresis) below 0.2 C, or the heater switches on and off too often and wears out the relay.

Set the alarms apart from the set points; about 2 C above and below works well. An alarm only helps if someone hears it or gets the alert.

Controllers have a calibration offset: compare the probe with a reference thermometer and set the offset to correct it. These units are typically within 0.3 C of true. Under the IMARCS rule, any offset is also written on a label on the device, so everyone knows it.

Put the probe mid-water in a well-mixed spot, near the return but out of its direct jet. A probe next to a heater reads high, so the controller cuts the heat too early. A probe buried in sand or rock reads late.

IMARCS rule (Michael Maddox, President of IMARCS): a controller's critical failure point is its probe coming out of the water. Out of the water, the probe reads the air, and the controller acts on the wrong number. The probe must sit in the water, away from spots that misread, such as next to a heater.

To fix it: put the probe back under water in a mixed spot and fix it in place with a holder made for aquarium use (plastic, under the material rule). Then compare the controller with a hand reading (Module 5).

Two smaller heaters instead of one: if one sticks on, it's less able to overheat the tank before someone notices; if one fails off, the other keeps heating.

A separate controller adds a second layer. Set each heater's own dial 1 to 2 C above the target, so the heater's thermostat acts as a backup if the controller's relay fails. All-in-one aquarium controllers have failed with the heaters left on, so keep heater control redundant. A heater with an external thermostat on its own isn't redundancy.

A heater stuck on is the failure to avoid at all costs: a whole system can crash from overheating. Signs: temperature climbing past the set point, a heater light on when it should be off, and the high alarm sounding.

To fix it: unplug the heater first. Start cooling (section 13): fans over the water, lights off or dimmed, the room cooler. Then find which part failed: the heater's own light and thermostat, the controller's heating outlet, and where the probe is. Replace the part that failed, then check the temperature by hand. Cool the tank back down gradually, not with a sudden jump.

Signs: temperature falling, especially in a cold room; the heater light off; the low alarm sounding. Glass heaters often fail when power comes back after an outage, so check heaters after every power cut (Module 33).

To fix it: check the power first: plug, outlet and breaker. Then the controller: set point, the heating outlet, and the probe's position. Then the heater: its light, and any crack. Swap in a spare heater if needed. Warm the water back to the set point gradually.

Tank water is pumped through a heat exchanger around cold refrigerant. The refrigerant absorbs the heat, a compressor squeezes it into a hot gas, and a condenser with a fan releases that heat into the room. A controller switches the chiller on above its set point.

Because the heat goes into the room, a chiller needs ventilation. In a hot room or a closed cabinet, cooling drops fast. The flow through it must match the maker's requirement; check it with a bucket test.

Maintenance: clean the fan and condenser fins regularly, since dust blocks the airflow; flush calcium out of the heat exchanger as needed; never let it run dry. If it runs more than about 15 to 20 minutes in an hour, look for an undersized chiller, poor airflow or a cleaning problem.

Set the heater below the point where the chiller starts, with a dead band between them (section 5). Set the heater about two degrees below the chiller's trigger point. If the set points match, both can run at once, fighting each other, wasting power and shortening the life of both.

To check: watch both outlets on the controller through a day. If the heater and chiller lights are ever on together, widen the gap between their set points.

Moving air over the surface speeds up evaporation, and evaporation cools the water. Fans are a cheap way to cool, and can be run from the controller's cooling outlet.

The top-off replaces the evaporated water with fresh water, so it runs more often: keep its reservoir filled. Salinity only climbs if the reservoir runs dry or the top-off fails (Module 5). A fan near the water also spreads salt spray: keep it clean, mounted securely, with a drip loop on its cord (Module 2).

Air conditioning is the best way to keep a tank cool in the heat: cool the room and the tank follows. Other steps: fans over the water; lights off, dimmer or on for fewer hours; non-essential pumps off, but the return and flow pumps stay on; skimmer and air pump intakes in the coolest air; cabinet doors open; and a temperature monitor with phone alerts.

Sealed bottles of frozen water can float in a high-flow part of the sump or in the top-off reservoir, rotated as they melt. Don't add ice or frozen water straight into the system; sudden temperature shock can kill fish and corals.

Warm water holds less oxygen while animals use more (Module 5), so keep surface movement and aeration strong in a heatwave. Write the plan down and keep the supplies ready (Module 36).

Compare each thermometer and controller probe with a reference thermometer, in the same spot at the same time. If a device reads off by a steady amount, set its offset if it has one, or replace it. Write any offset on a label on the device; log forms don't apply offsets automatically.

Take the logged reading by hand, not from a controller's screen (Module 5). Keep a second thermometer to confirm any reading that's far from the last one before acting on it. Calibration in general is covered in Module 7.