Layout and Plumbing

Water flows over the teeth, the slots at the top of the overflow wall, into the overflow box. It goes down the drain into the sump: through the filter chamber, past the skimmer, and into the pump chamber. The return pump sends it back up the return line to the display. While the return pump runs, the loop never stops.

The teeth and the valve on the drain pipe together set the display's water level. The walls inside the sump, called baffles, set the level of each chamber before them.

An all-in-one (AIO) aquarium has its sump built into the back of the tank. Everything in this module works the same way on an AIO.

The display is set by the teeth and the drain valve. The filter and skimmer chambers are set by their baffles. The pump chamber is the only level that changes. Water lost, removed or added anywhere in the system shows up there. That's why a top-off sensor sits in the pump chamber (Module 5).

Water poured into the display doesn't stay in the display. It goes over the teeth and ends up in the pump chamber.

If the pump chamber gets too low, the return pump starts sucking in air with the water. This is aspiration: bubbles shoot into the display, the pump gets noisy and pushes less water. If the level keeps dropping, the pump can run dry.

An overflow box has a weir (the teeth) and drain pipes. It can be internal, inside the aquarium, or external, on the outside. Most need holes drilled in the glass for the drain pipes. Never drill a panel unless you know it isn't tempered (Module 11).

A hang-on overflow needs no holes. A box inside the tank skims the surface, a siphon tube carries the water over the glass to a box outside, and a hose drains it to the sump.

Its weak point is air. Bubbles collect at the highest point of the siphon tube and can join into an air pocket that breaks the siphon. Then the drain stops, but the return pump keeps filling the display, which can overflow. Keep the tube and boxes clean, and check that both ends of the siphon tube stay under water when the flow stops.

To clear bubbles from the siphon tube: keep both ends of the tube under water, and raise and lower the tube firmly until the bubbles come out. Some designs use a small pump to pull the air out and restart the flow after an outage. A float switch set to turn the return pump off if the sump drops too low also protects the pump from running dry.

A siphon is a filled tube that carries water up over a high point and down to an outlet below the water's surface, with no pump. It has to be filled before it starts. It stops when air gets in, or when the water levels at both ends match.

A drain pipe running as a full siphon is filled with water and runs quiet. A drain with air being pulled into it gurgles and surges.

When the return pump stops, the return line can siphon water backward from the display into the sump. A small siphon break hole in the return line, at or just below the water surface, lets air in and stops it. Keep that hole clear of algae, calcium deposits and salt; a blocked hole lets the back-siphon carry on.

A Durso drain is one standpipe with a small vent hole that stops it siphoning. It's an open channel, not a full siphon. Its weakness: there's no backup if the pipe clogs.

A Herbie drain has two pipes. The main runs as a full siphon, controlled by a gate valve. The emergency pipe sits higher and only takes water when the main can't keep up. A BeanAnimal drain adds a third pipe: a siphon, an open channel and an emergency.

The systems drawn in this course use two pipes: a main and an emergency. In normal running, the emergency pipe is dry. Water in it means something is wrong.

The goal: the main runs full and quiet, and the emergency stays dry.

Too open: the main drains faster than water arrives. The box level drops, air is pulled into the main, and it gurgles and surges. Too closed: the main can't keep up. The box level rises, the emergency starts taking water, and the display level can rise.

Adjust the valve in small steps and wait for the level to settle before the next step. If the valve has to be closed more than halfway, slow the return pump down and start again. Algae, snails or debris across the teeth, or a clogged strainer on the main, also raise the level: clean the teeth before you touch the valve.

When the return pump stops, from a power cut or a pump failure, the display drains down until its surface falls below the teeth. The return line back-siphons until the water drops below the siphon break hole. All that water goes into the sump. This is the drain-down.

The sump has to have room for it. The max fill line marks the highest the pump chamber should ever be in normal running. The space above it isn't empty space; it's saved for the drain-down. A sump filled above the line, or a blocked siphon break hole, puts water on the floor.

When the power comes back, the return pump refills the display from the sump. The skimmer may overflow its cup for a while after a big level change. Module 33 covers power cuts in full.

In the US, rigid PVC pipe is commonly sold as Schedule 40, sized in inches. A 3/4 inch Schedule 40 pipe has an outside diameter (OD) of 1.050 in, about 26.7 mm. Schedule 80 has thicker walls for added strength.

In Japan, PVC pipe is sold to Japanese Industrial Standards, for example thick-walled VP pipe, named by number. VP 20 has an OD of 26 mm. Other countries may use other standards again.

So a fitting made for one standard may not fit pipe made to another, even when the names look alike. Before buying or replacing a part, find out which standard the system uses, and check the outside diameter.

A pump's rated flow is measured with nothing connected, at zero head. Head is the resistance the pump has to push against: lifting the water up, and pushing it through pipe, elbows and fittings. The more head, the less flow. For example, a pump rated at 1000 gallons per hour (about 3800 liters) might deliver only 600 to 700 at 4 to 5 feet (about 1.2 to 1.5 m) of head.

A pump curve is the maker's graph of how much the pump delivers at each head. As head rises, flow falls. At the shut-off head, the pump moves no water at all. To know what a pump will really do, work out the system's head and read the flow at that point on the curve.

Rules of thumb for head: each 1 ft (0.3 m) of rise adds 1 ft, each 90 degree elbow about 1 ft, each 45 degree elbow about 0.5 ft, and each 10 ft (3 m) of flat pipe about 1 ft. Pipe smaller than the pump's outlet, and reducers, also cut the flow. The flow sent up must never be more than the drain can carry back down. Module 13 covers pump types.

Slip (socket) fittings are glued with PVC cement. Dry-fit the parts first. Clean and prime both surfaces, cement them, push the pipe fully in with a quarter turn, and hold it about 30 seconds so it doesn't push back out. Then let it cure for the cement maker's time before water goes through it.

Threaded fittings don't take cement; use thread tape if needed, and don't overtighten, which can crack them. Elbows (90 and 45 degree) change direction, tees split a line, couplings join two pipes, and reducers change size, which slows the flow.

A union lets a joint come apart by hand, so equipment like the return pump can be removed. A bulkhead carries a pipe through a hole in the tank or sump: the gasket goes on the flange side, normally inside, on the wet side. Tighten it by hand plus a quarter turn, and never connect plumbing to its outside threads, which are only for its nut. Barb fittings connect flexible tubing: the ridges grip the inside of the hose, and a hose clamp holds it.

An adapter joins a slip end to a threaded one: a male adapter has the thread on the outside, a female adapter on the inside. A flexible coupling is a rubber sleeve with a band clamp at each end. Loosen the clamps, slide the sleeve over the plain ends of both pipes, and tighten the clamps. Flexible couplings are made for gravity drains, not pressure lines, so never use one on a return line. Check the clamps that come with a coupling: under the IMARCS rule, use 316 stainless or plastic clamps (section 11).

To fix a leaking joint: a threaded joint can be undone, cleaned, given fresh thread tape and tightened again, without overtightening. A cemented joint can't be undone, because the cement softens and fuses the parts together. Cut it out and replace the fitting, joining in new pipe with couplings. A sealant smeared over a cemented joint is only a stopgap. A leaking bulkhead: lower the water below it, take it off, check the gasket is whole and on the flange (wet) side, and refit it hand tight plus a quarter turn. A leaking barb: push the hose fully onto the barb and fit or tighten its clamp. Then test it again (section 14).

Every flexible tubing connection is secured with a hose clamp. Common types: a worm drive clamp, where a screw pulls a slotted band tight; an ear clamp, pinched shut with a special tool so it can't be undone; a spring clamp, opened by squeezing its tabs with pliers; and plastic clamps that ratchet shut.

IMARCS rule (Michael Maddox, President of IMARCS): everything in a system is plastic, titanium or 316 stainless steel. Nothing else. That includes clamps, screws, brackets and fittings.

Even 316 stainless isn't rust-proof in salt water. It can pit, especially in crevices, such as under a clamp band or a gasket, and in still water. Use plastic clamps for connections under water. So check every metal part when you do routine work.

To fix: a clamp showing rust comes off and is replaced with a plastic or 316 stainless one. A clamp of unknown metal is replaced the same way. Tubing that has gone hard or cracked is replaced (Module 11). A hose that has slipped back on its barb is pushed fully on and clamped again.

A ball valve turns flow on or off with a quarter turn of the handle. It's typically used on the return line. Cheap ones can get stiff and hard to turn over time. A gate valve raises and lowers a flat panel with a handwheel, so it can be set finely. It's the valve for drains.

A true union valve has a union at each end, so it can be taken out for cleaning without cutting pipe.

A swing check valve closes a flap when the water reverses. A wye check valve has a Y-shaped body with a removable part for cleaning. Fit unions on each end of an in-line check valve, so it can come out for cleaning.

A check valve lets water flow one way only. On a return line it's meant to stop back-siphoning when the pump stops. But it can fail to seal: salt and debris get in the way. It needs regular cleaning, and it's never the only defense against a flood. The siphon break hole and room in the sump are still needed.

To clean a check valve: switch off the return pump, undo the unions (or the wye's cap), take out the valve or its moving part, clean off salt and debris, and refit it. Run the pump and check for drips.

A return manifold is a main pipe, the trunk, running up from the return pump, with branches teed off it. Branches can feed the display, reactors, a chiller, a UV sterilizer or a refugium. Each branch has its own valve.

To set it up, open the display return fully, then turn down each other branch to the flow its equipment needs, and check each output. Every branch takes water from the same pump, so after changing any valve, check every output again.

Growth inside pipes and reactors narrows them over time, so the flows drift. Check the outputs regularly, and label each valve so everyone knows what it feeds.

First, the cement has to cure. A typical cement maker's chart gives 1 to 2 hours for small pipe in warm conditions before pressure testing, longer in the cold, and 50% longer in damp or humid weather. Follow the maker of the cement you used. Silicone and epoxy have their own cure times (Module 11).

Then fill the system with fresh water, no salt, and run it for at least a day. Check every joint, fitting, bulkhead and valve for drips, and look for a loose fitting. Switch the return pump off and watch the drain-down: the sump must hold it, and a hang-on overflow's siphon must hold too.

Fix any drip before salt water or animals go in, using the fixes in section 10. A drip doesn't stop by itself, and tape over a leaking joint isn't a repair. Pipes running near electrics need extra care (Module 10).