Aquaria

Aquarium: These are great tools for the imagination, as well as being a simulation of a natural ecosystems and the dynamic processes that unfold within it. They are particularly popular since they are easily available to interact with inside the comfort of one's home. A 20 gallon "long" aquarium has an optimal height/width/depth ratio. The aquarium I am setting up is intended to display reproducing animals that display the dynamic transformational processes of life. 

Occupants: These will include guppies, dwarf clawed frogs, freshwater crustaceans like scuds (Gammarus) and ghost shrimp, and a variety of plants (currently Rotala, Ludwigia, hornwort, Java moss, and duckweed). There are several things aquarium animals need to survive. In particular, caring for the offspring of reproducing animals, like very small fry or tadpoles, can be challenging. They may need small live foods like Artemia, Moina, daphnia, green water, and the "aufwuchs" that can grow on submerged surfaces (like Indian almond leaves). The fry of livebearers are large compared to most fish however and can usually eat the same food they do. But if you stick to the larger adults it should be fairly easy.

Lighting: Lighting is important for planted tanks, which are extremely popular and attractive. Many fixtures can cause shadowing in the corners, so pick an LED fixture that will provide the right spectrum of light and reach all your plants, these work well in combination with a full glass canopy, such as the "Finnex Planted+ 24/7 ALC". Setting a timer for the lights to be on between 8 to 12 hours per day is best, depending on the home schedule of the viewers. 

Filtration: There are many options from almost none (Walstad method) to moderate or higher, depending on the water properties and circulation levels desired. I've opted to use an undergravel filter plate and a "powerhead" pump. Many other options exist, such as "hang on the back" (HOB) filters, canister filters, and air pumps to circulate water. The undergravel filter and powerhead combination was chosen to prevent small animals from entering the filter inlet (video). Some people make their own PVC DIY UGF. A set of simple plans are available both of here and here. And powerheads are quieter than air pumps, while also avoiding the external hoses and airlines of canister filters and air pumps, or the space requirements of hanging filters. Just ensure that the inlet is able to fit the standard one inch "thinwall" clear rigid PVC tubing that is commonly used for the lift tubes on most models of undergravel filters. The water return will also need to be directed in a way that prevents excessive water flow from disturbing the smaller animals. I am currently fitting my outlet to a PEX multiport that serves to diffuse the force of the water flow.

Two companies that have made powerheads for many years are Marineland (which later became Cobalt and now Newa), and Aquaclear (Hagen). The Newa MP400 is a 106 gph pump, and there's plenty of discussion about that brand on the Reef2Reef forum. The Aquaclear Powerhead 20 is a 127 gph pump (and impeller). I have an older Marineland 550, which is a 145 gph pump that just needs a new impeller to restore it's quiet operation. As these are currently unavailable I'll switch to the Newa MP400. With more plants and fewer fish (Walstad method) the 30-55 gph rating of Zoo Med's "318 filter" is at the lower end of what's possible. 

Water surface agitation reduces the build up of a biofilm composed of bacteria and decomposing organic material (like proteins and fats). This is sometimes consumed by snails and shrimp, if you have them. "I have noticed a few shrimp swimming upside down under the water surface, I assume they are eating this biofilm," as one person anecdotally posted to a shrimp forum. It is not good for fish however, so a variety of tank inhabitants (fish and freshwater inverts) each occupying a different ecological niche, with a moderate overall bioload and sufficient water movement (pump maintaining flow rate) should be established. Some tanks use an "overflow" device, a protein skimmer, or an air pump producing fine bubbles to remove a biofilm. But this added complexity is nothing that a simple pump with a diffused water return outlet shouldn't be able to accomplish by itself. 

Operating costs: If you have an aquarium heater that uses 150 kWh/year, and the electricity rate is 22.54 cents/kWh, then it costs $33.81/year to use.