Can I please get feedback and help for my canopy design?

[strich]

I’m in the early design phase for a custom canopy for my Waterbox 130.4 reef tank (1200 x 600) and wanted to sanity check the approach before I start building.

The plan at the moment is to build the canopy frame from 2020 extruded aluminium with removable exterior panels for access/feeding. The canopy would probably have around 20cm of height internally and house a couple of fairly powerful LED reef lights.

One of my main goals is actually to REDUCE evaporation rather than maximize ventilation. I’m in Brisbane, Australia, and evaporation can get pretty wild here. I’d like to keep humidity trapped inside the canopy as much as reasonably possible to improve stability and reduce top off demand.

Because of that, I’m approaching this less like a ventilated hood and more like a controlled humidity chamber. I’m assuming condensation will definitely happen, so instead of trying to eliminate it entirely, I’m thinking about intentionally managing it.

Current ideas:

• Slightly sloped internal roof panels so condensation runs toward the rear
• Internal drip lips/gutters to direct condensation back into the tank
• Keeping the removable front panels mostly outside the humid barrier
• Adding fixed internal condensation baffles/lips behind the removable panels to direct drips back into the tank
• Minimal ventilation unless heat becomes an issue - The roof panel will be removable so I can do that if I have to

A couple of questions I’d love input on from people who’ve built enclosed canopies before:

1. Has anyone intentionally tried to run a more sealed/humid canopy to reduce evaporation? Did it work well long term?
2. How aggressive does condensation actually get inside enclosed reef canopies with LEDs these days?
3. Are there known good ways to create drip rails/gutters that don’t eventually become horrible salt creep traps?
4. Has anyone used aluminium extrusion for a canopy long term? Any issues with corrosion around salt humidity?
5. Any major downsides I might not be considering besides heat and possible pH reduction from reduced gas exchange? I do have a skimmer I run 24/7 and I could running additional aeration in the sump if I need to.
6. Does anyone regret going too enclosed with their canopy?

I’m aiming for a pretty clean industrial/minimal look rather than a traditional timber hood.

Would really appreciate any photos, lessons learned, “don’t do this” warnings, or clever design ideas before I start prototyping.

 

[BeanAnimal]

The major driver of evaporation is airflow at the water surface.

I personally would not want to use a hood to trap significant moisture unless the fixture were fully IP rated. Instead I would vent the canopy enough to allow it to have only a slightly higher RH than the room in hopes of preventing condensation.

I would work to keep airflow low at the water surface and still move enough air to keep the lights cool. The lights will generate a tremendous amount of heat in an enclosed canopy.

 

[TheCoralSwap20]

Few thoughts before you start cutting aluminum!
Lights — are yours rated for humid/splash environments? Most modern reef LEDs are.

Heat — 20cm internal clearance with powerful LEDs and minimal ventilation is going to get warm. What lights are you running? If they have onboard fans (like the AI Primes I have) they're already moving air and generating heat in an enclosed space. Summer ambients here could push that canopy interior pretty hot, which works against your tank temp goals.

Cords — make sure every cable entering the canopy has a drip loop

Salt creep in your gutters — Any horizontal surface inside a salt-humid enclosure will build up over time, especially with temperature cycling. Steep angles, smooth surfaces, and making those sections genuinely easy to pull out and rinse are your best options. If the gutters are hard to access they'll become a maintenance nightmare.

Aluminium extrusion — use stainless hardware throughout, not standard T-nuts and bolts. The T-slot channels will trap moisture and salt, and standard fasteners will seize or corrode over time. The extrusion itself will be fine with anodising, the fasteners are the weak point.

Two attachment points - If your not planning on putting anything of significant weight on top, you'll be okay. But as soon as you place - say a 5 gallon bucket on top, that will stress those two vertical points, maybe not brake but why test it. Place a diagonal piece to create a little triangle. That'll give those two vertical points a lot more strength.

The sealed humidity approach is smart for your situation — just make sure heat doesn't become the thing that forces you to ventilate anyway and undoes the whole design as @BeanAnimal mentioned.

 

[strich]

The major driver of evaporation is airflow at the water surface.

I personally would not want to use a hood to trap significant moisture unless the fixture were fully IP rated. Instead I would vent the canopy enough to allow it to have only a slightly higher RH than the room in hopes of preventing condensation.

I would work to keep airflow low at the water surface and still move enough air to keep the lights cool. The lights will generate a tremendous amount of heat in an enclosed canopy.

Adding a small fan directed at the top of the LEDs isn't out of the question for sure.

 

[BeanAnimal]

Adding a small fan directed at the top of the LEDs isn't out of the question for sure.

I think you may be severely underestimating the amount of heat that you are dealing with.

How many watts is your lighting?

 

[Dorsetsteve]

What you want is a cover glass. Then mount your canopy above the cover glass and ventilate it.

 

[strich]

What you want is a cover glass. Then mount your canopy above the cover glass and ventilate it.

I could although I would expect the glass to get a salt film and condensation very quickly and rapidly reduce the lighting requiring cleaning very often. I'd love to hear anyone's experience doing this!

 

[BeanAnimal]

Given your responses, it sounds like you may only looking for answers that validate your design choice. Understandable, but I don’t think you have fully considered the heat and I am not sure that the amount of evaporation saved will be worth the added complications.

Drip rails will be a mess of salt deposits. The anodic layer will eventually break down and expose raw aluminum. So stainless or plastic would be more appropriate.

Yes, there would need to be a lip or flange inside the aquarium rim otherwise where there will be condensation and creep where the canopy meets the tank. Even then, there will be air movement at the interface, and salt creep.

The lights will gather condensation inside and out, along with salt creep.
As I mentioned prior, the lights will need to be IP rated, but failure may still occur because even IP67 not prevent salt creep from eventually wedging through.

 

[Fish Fan]

I get that you are in Brisbane, Australia, but your plan to basically seal the canopy to trap in humidity is going to cause your lighting to rot

Why not go with a more traditional screen cover that allows moisture to escape, and simply add an Auto Top Off (ATO) system to handle the evaporation?

 

[BeanAnimal]

To that end, I am not sure why evaporation in Brisbane would be worse.

Brisbane is sub tropical and humid most of the year. The climate thwarts evaporation, it doesn't drive it. If the home is AC cooled, then the RH in the home will be lowered (at best) to what is considered normal.

I am all for helping with the design, but I think it is going to create unneeded complications for little gain.

 

[JGT]

I agree. I think you’re overthinking/overcomplicating the design. I’d build the canopy with no top for full ventilation. Since it’s up high you won’t even see the top of the canopy.
You could cover the top of the tank with glass or acrylic. It won’t have a significant impact on your PAR but I don’t see the point. Let your ATO handle the evaporation.

 

[BeanAnimal]

Mentioned earlier: air movement at the air-water interface is the primary driver of evaporation.

The thin (atoms) layer of air at the water surface becomes saturated with moisture. Moving this air away allows dryer air to take its place. The more efficiently this "blanket" of air moves, the faster the evaporation occurs.

Smooth laminar flow is far more efficient than turbulent or random flow. That is why blowing a fan across the water surface is far more efficient at driving evaporation than pointing the fan down at the water surface.

The OP's plan is to trap all of this moist air in the hood so that the process slows by not allowing dryer air to reach the water. I Think the better plan would be to vent the hood, preventing heat and moisture buildup, while working to minimize the direct airflow to the water surface. Even something as simple as a mesh top will significantly reduce laminar airflow at the water surface.

 

[strich]

Given your responses, it sounds like you may only looking for answers that validate your design choice.

Respectfully, I’d prefer to keep personal assumptions like that out of the discussion. I’m genuinely here to pressure test the idea and hear where the problems are, even if the end result is “don’t do it.” I do appreciate you continuing with the technical discussion afterwards though.

Thank you all for the advice so far. You’re all very likely right that I may be over-engineering this and that the goal itself may not be worth the tradeoffs long term.

I do already have an ATO, so refilling it once a week isn’t really the end of the world. My bigger concern is actually the tank being in our living room and trying to avoid dumping large amounts of humid air into that space.

There’s an air conditioner in the room which can obviously handle the humidity load, but my assumption was that once the AC starts drying the room air out, it’ll also increase evaporation from the tank and the two systems just end up fighting each other.

I’d definitely prefer a design that avoids needing to actively manage condensate if possible though, because you’re all probably right that drip rails/gutters/etc would become a long-term salt creep and maintenance battle.

@BeanAnimal your comments about optimising airflow without disturbing the saturated layer directly above the water are really interesting. I’m now wondering how much difference a semi-open canopy or partially baffled top might make compared to either extreme of fully enclosed vs fully open.

 

[BeanAnimal]

I do already have an ATO, so refilling it once a week isn’t really the end of the world. My bigger concern is actually the tank being in our living room and trying to avoid dumping large amounts of humid air into that space.

There’s an air conditioner in the room which can obviously handle the humidity load, but my assumption was that once the AC starts drying the room air out, it’ll also increase evaporation from the tank and the two systems just end up fighting each other.

The concern is understandable. Yes, the tank and room interact.

Is the AC isolated to the room with a local thermostat, or is it the whole house?

The distinction will somewhat change the dynamic.

@BeanAnimal your comments about optimising airflow without disturbing the saturated layer directly above the water are really interesting. I’m now wondering how much difference a semi-open canopy or partially baffled top might make compared to either extreme of fully enclosed vs fully open.

I think it will make a considerable difference, just as aiming fans different does or adding and removing a mesh top does.

My tank is open top and my sump is open top. I don't currently track evaporation, but used to heavily rely on fans for forced evaporative cooling. A simple computer case fan blowing across the surface easily double ATO usage. At the height of my MH usage I was easily evaporating maybe 3-5 gallon per day by use of multiple fans over the tank and one in the door pulling the air out of the room. Our whole house AC kept the overall humidity down, but I could tell in stagnant areas of the home that moisture was accumulating.

 

[strich]

Is the AC isolated to the room with a local thermostat, or is it the whole house?

The distinction will somewhat change the dynamic.

The AC is isolated to the room the tank is in, asking with our lounge and kitchen.

So if I continue to design my canopy with a removable top in a few pieces then the first test could be to see if I can reach a good reduction of evap with no condensation.

 

[BeanAnimal]

I think that is a decent plan.

You may also want to think about building a cooling channel above the lights but is baffled to prevent updraft from pulling air across the water. Options would be open top above the lights with baffles along the sides, or a closed duct open on the ends open on the bottom to the lights. This may not move as much heat.

I can explain either in more detail If that doesn't make sense. The mostly dead space would the have adjustable vents to balance the humidity and slow evaporation, but keep it below the condensation point.

 

[Dorsetsteve]

I could although I would expect the glass to get a salt film and condensation very quickly and rapidly reduce the lighting requiring cleaning very often. I'd love to hear anyone's experience doing this!

There will be a reduction in light albeit minimal and an easy to solve issue.
Condensation will accumulate at night when the lights are off, this will help reduce the salt deposits, once your lights come on the heat of them the condensation will clear.

Cover glasses in the U.K. used to be the norm, many people use them in winter to reduce mould in the house because of the aquarium. Having a massive bucket of water that’s warmer than the air is a good way to cause problems. We know a thing or two about humidity and damp over here