Design options for open systems

  • #1
Building your own open system (sump, wet/dry, refugium, whatever you want to call it) can be confusing, especially in the design phase.

What sections will you put in, and in what order do you want the water to flow through them? How will the output of one affect the effectiveness of others? Are there any that you should avoid because of the animals/plants you choose to keep?

Let us see what the options are and what they do.

Primary purpose: Increase water volume
Intake: Water
Structure: Anything that holds water separate from the display tank
Output: Water
The sump is the most basic open system. It is pretty much just a volume of extra water to increase the total size of your tank’s biosystem. The increased volume dilutes pollutants and reduces fluctuation in temperature and water parameters. Bigger tanks are more stable and a sump is added stability. People often put heaters and other equipment into the sump to keep it out of the display tank. The word sump is also used to refer to a complete multI sectional open system.

Primary purpose: Biofilter
Intake: Water with dissolved fish waste and ammonia. Particulate waste should be removed beforehand as it will foul the biomedia.
Structure: A trickle plate or spray bar spreads water evenly over a compartment filled with biomedia, the bulk of which rests over the water line in the open system. Ammonia is turned into nitrite, and then nitrite is turned into nitrate. Oxygen is added, Carbon Dioxide is removed.
Output: Water rich with nitrates and oxygen, but reduced CO2 levels.
The wet/dry filter is a home for aerobic bacteria. In freshwater systems this is composed of bioballs, sponges, ceramic biomedia, pretty much anything to provide surface area. In saltwater they often use live rock rubble, small chunks or unattractive pieces that they do not want in the display tank. As the water trickles down through the biomedia the co2 gasses off, and oxygen dissolves into the water. The bacteria use the oxygen to thrive and process ammonia>nitrite>nitrate at an amazing pace. If non-dissolved waste is allowed into the wet/dry compartment it can build up in the biomedia and turn the system into a “nitrate factory”. Prefilter the water to reduce biomedia maintenance. The term Wet/Dry, like the word “sump” is often used to describe an entire open system; most likely because you can buy prefab wet/dry filter systems which include a mechanical prefilter and a sump for underneath the actual wet/dry section.

Baffle Compartments
Primary purpose: Filtration and control of water depth.
Intake: Water containing something you want removed.
Structure: Sections of the open system divided by baffles which force the water to flow up or down through each stage in sequence. The stages are used to hold changeable media, usually in bags or baskets for ease of replacement.
Output: Water with less of the substance you want removed.
As the water flows up or down through these sections it can be forced through whatever you decide to put in between the baffles. This is where the open system can easily emulate a power filter or canister’s multI stage filtration. Carbon, filter floss, sponges, pot scrubbers, zeolite, biomedia… You can put in whatever you need whenever you need it. They can each have their own compartment, or each section can have layers of different items stacked into them. You can even put in things you want added to the water such as crushed coral or peat, or heat if you put your heater in a baffle (be sure to use a section that never drains) to ensure good flow over it. On the fly customization and versatility, baffles can do in miniature the tasks of most of the other compartments in this list. The reason they are getting a separate mention is their changeable nature. The baffle that is full of floss today for polishing your water could be full of carbon tomorrow to remove meds.

Primary Purpose: Diverse. Organic filtration, nitrate export, PH cycle balancing, livestock seclusion, food source
Input: Water, the condition of which depends on what the refugium is being used for. Often Light.
Structure: From a totally bare box to a fully functioning minI aquarium, depending on need.
Output: Cleaner water if being use for filtration. Small critters if it is being used as a food source.
I was tempted to put this as a subdivided section, but since these functions can all be combined in the same compartment, I left it as one. For Organic filtration freshwater would use lots of plants that feed primarily from the water column, saltwater would use live rock or a deep live sand bed. For nitrate export, put in fast growing plants and trim often. To balance the day/night PH cycle: run the lights on the refugium on a schedule opposite of the lights on the main tank. The refugium can be used as a holdover for new fish between quarantine and the main tank, a place where they are separate but exposed to the same water. It can also be used for non-contagious ill fish as a safe spot away from bullying, but without the stressful acclimation of being moved to a different tank. Small food animals can be kept in the refugium to allow a colony to thrive without suffering from constant predation.

Mechanical filter
Primary purpose: Remove non dissolved waste and detritus from water
Intake: Water with solid items to be removed
Structure: Usually a mesh, grate, perforated plate, open celled sponge, or other device that lets water flow through while obstructing non liquid items.
Output: Water with solid items strained out.
Not so much a compartment as a functional divider between compartments, the mechanical filter is stopping solid items from going further into the filtration system where they could cause problems. Mechanical filters range from the size of eggcrate to catch leaves and dead fish down to micron filter pads. The smaller the particles that a mechanical filter will block, the faster it will clog. For that reason they are often layered or arranged so that the water passes through them in order of descending filtration rating. A coarse sponge before a 50 micron filter pad will make the pad last longer. A coarse sponge AFTER a 50 micron filter pad will catch nothing and is basically just biomedia. In an open system mechanical filters can be found everywhere. The teeth on the overflow box. The filter sock the overflow drains down into. The pads on top of the wet/dry’s drip plate. The sponges tucked in the bottom gap between baffles. The intake guard on the return pump. Even a totally unobstructed, large, slow moving sump will have things settle to the bottom. Pretty much everything in the open system will act as a mechanical filter if given the chance. The question is what parts do you NOT want acting as a mechanical filter. Before the water gets to those sensitive areas, make sure you have filtered out any debris larger then what you want passing through those sections.

Bubble trap
Primary purpose: Remove or reduce the size of bubbles
Intake: water with bubbles
Structure: a series of baffles spaced closely together in which bubbles are trapped, popped, or reduced in size
Output: water with no bubbles or only micro bubbles.
This small structure is not really a compartment. It’s another functional transition between compartments. It is usually located on saltwater systems before whatever compartment houses the intake pump for the skimmer.

Protein skimmer
Primary Purpose: Remove dissolved organic compounds before they break down into ammonia.
Intake: Water with dissolved organics and no large bubbles
Structure: A pump which brings in water and mixes it with micro-bubbles to form a bio-foam which then climbs a thin walled tower and deposits its biological load into a collection cup.
Output: Water with dissolved organics removed
Protein skimmers remove organic wastes from the biosystem before they have a chance to decay and feed the nitrogen cycle. The stuff taken out at this early stage does not have to tax the other systems in the tank. Large bubbles inhibit the foam climb, so generally the compartment that contains the Protein skimmer’s intake will be fed through a bubble trap. Skimmers are not often seen in freshwater aquaria.

Turf Algae Filter
Primary Purpose: Remove Nitrates and Phosphates
Intake: Raw tank water
Structure: Water runs over a flat algae covered surface with good airflow and lots of direct light.
Output: Water with Nitrates and Phosphates removed
This is a method of algae control best compared to fighting fire with fire. Basically you are maintaining a smal but super powered algae farm to outcompete algae in your display tank by consuming all the resources it would need to grow.

Top Off Reservoir
Primary purpose: Keep your water level steady and for saltwater, your salinity stable
Intake: Clean fresh water prepared appropriately for the tank in question
Structure: anything from another tank to a simple jug, connected with a valve controlled by water level
Output: top off water
For freshwater this is not a common item, water level is kept constant with regular water changes unless you are in a really high evaporation situation. For saltwater this is very important, as water evaporates it leaves it’s salt content behind, raising the salinity of the system as a whole. The water provided by a top off counters dangerous water parameter swings in salt water aquaria.

Return pump enclosure
Primary purpose: Avoid overflow of display tank
Intake: Water that has made its way through your open system
Structure: A section sealed on all four sides at the bottom, with water overflowing on one side at a specific height. Return pump positioned in the chamber sometimes on a riser or stand.
Output: Water under pressure for the trip back to the display tank.
This is a reduced surface area section of the open system with a baffle on the input flow into it. The idea is that is the main tank stops sending water into the open system for any reason that this compartment would stop getting water flowing into it shortly thereafter. Then because the surface area is small compared to the surface area of the main tank the water level in this section will drop rapidly while only raising the water level in the main tank a little bit. The goal is for the pump to either hit its auto-shutoff point (if it has one) or run dry before the main tank can overflow. A pump running dry will usually destroy the pump rather quickly, but a pump is nearly always cheaper than the damage that would be done by a large scale overflow.

__________The reason for the thread____________

I am using the term open system to apply to sumps, wet/dry, refugiums, etc... From my research they are often combined and overlap quite a bit, the main connection seems to be that water leaves the main tank goes into a separate tank(s) then comes back to the main tank modified by its side trip. The only term I’ve found that really embodies them all as a group is “Open System”

I'm getting ready to design and build an open system filtration unit and would like some help clarifying what each part can do. I'm not sure what all sections I want/need for my particular application and what order I should be putting them in. I looked for this kind of list and did not find it. I'm going to list the different parts I know about, and what I think they do, then as people correct my mistakes I'll edit them to be more clear, the format is going to be odd, but you will catch on I'm sure. Mods, feel free to edit the main post at will. It will need a bunch of links to appropriate threads and articles before it is really useful, but I’ve typed enough for today.

I really want input on any compartments or sections I missed and what other affects the listed ones have on your water. What does a skimmer do to your dissolved oxygen and co2 levels? What affect, if any, does a wet/dry have on your dissolved nutrients for your plants?

Order input would be nice as well, things like:
A wet/dry section is a bad idea right before a heavily planted refugium because it will gas out all the CO2.
A wet/dry section is a good idea right before a heavily planted refugium because it will provide lots of nitrates for the plants to feed on.

See, I don’t know which is true. If they both are, which is more important?

I was surprised that I could not find an article like this on any of the various aquaria sites I follow. I’m 90% certain that within a few minutes of posting this someone will point me to a much better written version with all the information I need. Even so, typing this all in has helped me find holes in what I do know, and thus will let me ask better questions to put together the project I have in mind… But that project is for another thread.

  • #2
I haven't seen an article like this, but I haven't been looking specifically for one, just general information and research.

Thanks for it, though. Sometimes I want to post a thread saying, "walk me through it like I'm a dummy..."

  • #3
Great post. I am also in the process for designing an open system, so I will be watching this thread. I am particularly interested in the order of sections and how they affect one another.
  • #4
Great write up as I have been looking for something very similar. Would great sticky in the DIY section as it is now, and perfect as it gets polished up.
  • Thread Starter
  • #5
My running plan for my freshwater open system in a 29 gallon tank, it leans heavily on a baffle series as I change my mind a lot and want the versatility:

overflow (gentle design to pass down any fry that squeeze into it)>
refugium (19 gallons of the tank, Heavily planted and well lit. Possibly one betta>
mechanical filter leading into the baffle area (a simple grate)>
First baffle, down flow, mechanical filtration (sponges of decreasing pore size)>
Second baffle, up flow, open space for the heater>
Third baffle, down flow, biomedia (ceramics, not decided on shape)>
Fourth baffle, up flow, Filter floss for polishing (carbon under the floss when needed)>
Return pump enclosure>
spray bar back into to the main tank.

The open system I'm currently working on is for a freshwater tank that will contain mainly livebearers. The main point of this open system is not actually to act as a filter, but an aquatic garden. I figured why not let the fish above it feed the plants, and let the plants clean their water. Plus with the whole thing acting as a sump, the increased total water volume will help with livebearers tendancy to keep a tank overstocked as fry grow out large enought to rehome.

I've designed an overflow that will skI'm the surface, and if a fry manages to wiggle into it, their ride to the open system underneath would be fairly gentle. I'm dumping the water straight into the refugium in case some do take the waterslide, they will not die on a trickle plate or mechanical filter. Plus I want the water coming in at it's worst to feed the plants.

The refugium will be crazy planted. I'm thinking a plant friendly substrate and DIY CO2. I'm building the troffer for the lights now, the ballast I already have will provide 51watts (3 17watt t8's), and I'm considering adding a couple of in little aimable swivel sockets for spot lighting.

The first mechanical filter is pretty much to keep leaves out of the filter area.

The first baffle will usually be sponges. I have a bunch of old aquaclear sponges laying about, and they are pretty cheap. I might put a couple pot scrubbies on top of the sponge stack to catch the biggest chunks.

The second baffle will be tall enough and always full, plus it will be pretty central to the tank, so I'm going to toss the heater(s) for the whole system in there for good water flow over them, and to warm the water for...

The third baffle will be biofiltration. I kinda doubt much will make it through the plants, but if it does the media here will have nice warm water flowing over it for good BB growth.

The fourth baffle will usually be used for floss, but I can toss carbon under the floss when needed to clear our meds other odd chem polutants. I wanted this stage after the biofilter as this will be the most often changed section, and I wanted as little of my BB growing here as possible. Hopefully by this stage there will not be enough food for them left in the water to make changing my floss have any effect.

The return pump enclosure I currently have planned will be 4"x6" and 14" tall. I'm not sure on my pump yet. I know the one I'm looking at will fit, as will the powerhead I'm starting with, but I'd rather not have to rebuild the whole system to accomidate a bigger pump if it turns out I need one, so I'd love comments on common pump dimensions before I begin my build.

Most of the things I listed in the original post do not actually apply to my needs, but I tossed them in anyway hoping to start discussions on people's plans and providing a framework to allow easy discussion and comparisons. I was originally planning on a wet/dry section, but with the gassing out CO2 I don't think it would be good for our plants.

Feel free to toally tear any part of this apart or rearrange at will, I'm looking for all input. I have not even bought most of the supplies yet for this project, just the tank itself. I made a 1/4 scale mockup out of paper, air tubing, and misc bits of junk and it looks like it should work ok, but this is my first open system, so who knows.
  • #6
Sound good. I'll have to take notes. I have a 29 gallon as well.
  • Thread Starter
  • #7
I've gotten the glass cut for my dividers, and I'm working on balancing the flow/noise from my overflow design. Once I have it finished and operating for a while I'll toss up some pictures and update the original post with my findings.

I was really hoping to get some more criticism and have people point out places where I'm wrong so that I could improve the info in the post. I'm basically a noob at this, and just put down what I was able to find out from research. It would be nice to have some input from people with real world experience.

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