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Outdoor Guppy Tub
Outdoor Guppy Tub

Outdoor Fish "Tubbing"

Keeping fish in small, temporary outdoor ponds or tubs is often referred to as "tubbing" among fishkeepers. The most popular fish to keep in tubs are probably live-bearers. This includes guppies, Endlers, mollies, platys, and many other species. These tubs are unfiltered and in many cases go an entire season without a water change. This summer I'm keeping guppies in a 100 gallon container in my back yard.

What Temperatures Can Guppies Survive Outside?

Unlike goldfish and koi, guppies can't survive outdoors in cold weather. While most sources will list the minimum acceptable temperature for guppies anywhere from 65°F - 72°F, they can tolerate water as cold as 60°F for short periods of time.

Where I live in Colorado, there is only about a 3 month window every year when temperatures are consistently warm enough for a guppy tub. The chart below shows daily average high and low temperatures specific to my area.

Colorado Average Monthly Temp
Colorado Average Monthly Temp

Water doesn't heat or cool as quickly as the surrounding air. This means the water in an outdoor tub usually won't reach the daily high or low temperature on a given day, it will drift gradually between them. The average water temperature should be near the center of the daily range. There will also be a temperature gradient between the water's surface and the bottom of the tub, assuming it is sufficiently large.

Actual Guppy Tub Temperature Observations

During the month of June I took temperature readings of my guppy tub at least once every day, up to 3 observations per day, for a total of 55 observations. The data I collected is shown in the chart below. You can see that on very hot days the water temperature (measured using a floating thermometer at the surface) reached as high as 86 degrees. This only lasted a few hours until the sun set, but I am planning on setting up some afternoon shade for the tub going into the hottest part of the year. As you might expect from historical weather data, the average water temp observed in June was 71.5°F.

Note: All of these temperature observations were made at various times throughout the day between 7:00 AM and 7:30 PM.  The highest temperatures were observed in the late afternoon after several hours of direct sun.

Water Temperature of the Guppy Tub Throughout June 2019
Water Temperature of the Guppy Tub Throughout June 2019
High 86
Low 58
Average 71.5

I kept the guppies in an unheated aquarium indoors at 68°F - 70°F for several months in preparation for this project, during which time they continued to breed and grow. I did not observe any deaths during the month shown here, and saw new fry after about 3 weeks of the guppies being in the tub. Based on my observations, guppies are able to tolerate relatively large daily swings in temperature, as long as the extremes are not too hot (above ~90ºF) or too cold (below ~60ºF).

Outdoor Guppy Tub Container

I chose a 100 gallon Rubbermaid stock tank for this guppy tub project.

100 Gallon Rubbermaid Stock Tank
100 Gallon Rubbermaid Stock Tank

I've seen others use rain barrels, kiddie pools, pond liners, etc. I wouldn't use anything that holds less than 40-50 gallons, because water parameters are going to be more stable in a larger volume of water. You should also avoid any container that is too tall and skinny, as this will make viewing and catching the fish difficult. Stock tanks (horse troughs) are the ideal shape for a garden pond.

Guppy Tub on Day 1
Guppy Tub on Day 1

Outdoor Guppy Tub Plants

Floating Plants
Floating Plants

Plants are an essential requirement for outdoor fish tubbing. Since you won't be performing many water changes, plants will help to remove excess nitrogen. They also compete with algae for nutrients. A pond without any plants will quickly turn green after a few days of sunlight. Any aquatic or marginal plant could be used in an outdoor guppy tub project. Some common pond plants include water lilies and water lettuce.

Shop Pond Plants on Amazon

I set up this pond with some duckweed & water lettuce from my Endler breeding aquarium.  I also added a large portion of najas/guppy grass. Guppy grass can be grown either rooted or as a floater, and is often used in breeding live-bearers. Floating plants are a good choice for an outdoor tub because the roots provide shade and cover for the fish, and they don't require any substrate.

Adding Fish to an Outdoor Tub

Ideally you'd want to have an outdoor tub filled and planted for several days before introducing fish. This gives the water an opportunity to age in the sun, as algae grows and infusoria begin to develop. I added water from established aquariums to my 100 gallon stock tank, and let it sit for 3 days before adding any fish. As mentioned above, I also prepared my guppies by keeping them in an unheated aquarium all spring before they moved into the tub.

Guppies
Guppies

Maintaining Water Quality in an Outdoor Tub

Water Changes

In a perfect world, all water that evaporated out of a tub would be replaced by rainwater, and all wastes would be absorbed by the plants. Of course that's not the world we live in. You should check the nitrates in an outdoor tub just like you would with an aquarium, and do a water change if they rise over 20 ppm. I've found that a 30% water change every 2 weeks is adequate in my pond. This probably wouldn't be necessary if I had enough plants to entirely cover the surface.

Aeration

I use a solar powered air pump to oxygenate the water. I plan on going into more detail on this build in a separate post, but you can get the solar panel I'm using here on Amazon. You'll also need an air pump that can run off USB power, which I got from Aquarium Coop (https://www.aquariumcoop.com/). You can also buy them on Amazon. This pump runs about 10-11 hours per day (you know, solar) and does a good job keeping the water from getting stagnant.

This store-bought shelving unit is the perfect size for supporting a pair of 40 gallon breeder aquariums.
40 Breeder Rack
40 Breeder Rack

I've built a few DIY aquarium racks, but I wanted to go with a steel frame for my two 40 breeders to save space. Unlike a wooden frame, these steel supports lay flat against the sides of the aquariums. Steel shelving can also support a lot of weight - 800 lbs per shelf in this case. Water weighs roughly 8 lbs per gallon, so 40 gallons of water alone is 320 lbs. When you add the weight of the glass aquarium (58 lbs for a 40 breeder), substrate, heater, filters, etc. the total weight of one 40 gallon aquarium can be over 400 lbs.

Where to Get a Steel Aquarium Rack

Edsal Storage Unit
Edsal Storage Unit

These heavy duty storage units have been recommended by several people over the past few years as an affordable store-bought option for holding one or two 40 gallon tanks. This video by Aquarium Co-op from 2014 referenced a very similar rack that may or may not still be available from Lowe's. I purchased mine at Home Depot. Similar units are available from a variety of retailers, including this Muscle Rack on amazon. Fortunately 36" x 18" seems to be a fairly common shelving size, so it should not be too difficult for most people to find.

Aquarium Rack Assembly

The cool thing about these 5-shelf steel units is that they are really two units that stack. The kit comes with eight upright posts that are 3 feet long, which makes the unit 6 feet tall when stacked. If you didn't want one tank on top of the other, you could place both sets of uprights on the floor and have two separate aquarium stands.

First Aquarium in Place
First Aquarium in Place

For my application I only used 3 of the 5 shelves that came with the unit. It has to be assembled from the floor up, so the bottom shelf goes on first, followed by the first aquarium shelf. Because the dimensions are so similar to those of a 40 breeder aquarium, the tank has to be lowered into the posts from the top. This gets tricky when you get to the top aquarium.

Hacksaw
Hacksaw

In order to be able to lift the top aquarium above the tops of the posts, I cut about 6 inches off the front two uprights using a hacksaw. Cutting through the steel was actually easier than it looks because its not very thick. Once the cuts were made, I was able to lift the top tank up (with help) and slide it down into place.

40 breeder rack
40 breeder rack

Although two of the shelves were not used on this rack, I added their steel support sections to the sides and back of the unit to add stability. Without the extra bracing, the whole rack was somewhat wobbly. In the photo above you can see two extra 36" braces positioned a few inches below each aquarium. This keeps the rack from bowing or shifting under the weight of two full aquariums.

After both tanks were on the shelves I moved the unit into its place along the wall and finished the overflow plumbing before filling with water. I also painted the bottom shelf black to match the rest of the rack. The space underneath the tanks adds a lot of extra storage to the fish room. I keep my folding step ladder tucked next to the rack so that it's easy to access when I need to work on the top tank.

Bottom Shelf Storage
Bottom Shelf Storage

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Why Feed Live Baby Brine Shrimp?

Fish thrive when fed live foods often, especially when they are young. Live baby brine shrimp are a highly nutritious food for fish fry; full of protein and nutrients that dry flake food just doesn't offer. Newly hatched brine shrimp are very small, measuring less than 1 mm. Fish of most species are able to eat them within their first week of life. Additionally, fish love brine shrimp. Almost any fish will eat them live or frozen.

The photo below shows a newly hatched and strained batch of baby brine shrimp.

Baby Brine Shrimp in Coffee Filter
Baby Brine Shrimp in Coffee Filter

Hatching Brine Shrimp

Brine shrimp eggs are actually dormant cysts. They can stay viable for years if they are stored in a cool, dry container. When exposed to warm salty water, they re-hydrate and begin to hatch. Hatching baby brine shrimp is pretty simple. Below is a list of the materials you'll need to start your own hatchery.

1. Container

The optimal container for hatching brine shrimp has a tapered or conical shape. A very cheap and reliable option is to use an inverted plastic soda bottle. A 1 Liter bottle will work for small batches but a 2 Liter is more efficient. The photo below shows a 1 liter water bottle being used to hatch brine shrimp.

1L bottle brine shrimp hatchery
1L bottle brine shrimp hatchery

Another option is to purchase a specially designed brine shrimp hatchery like this one. This may be a good option if you want something sturdy that can be used for a long time.

2. Aquarium Salt

Brine shrimp, as the name implies, require a brine solution to hatch. The typical solution is about 1.5 tablespoons of salt per quart of water, or 25 parts per thousand of salt. Although you don't have to use aquarium salt, I like to use it because the large crystals are easier to work with without making a big mess. A large container is not very expensive, and will last a long time if you are just using it for this purpose.

Aquarium Salt
Aquarium Salt

3. Air

Hatching brine shrimp requires an air pump to tumble the cysts in the water and keep the solution oxygenated. You don't need an air stone. Just position the airline tubing so that the bubbles are coming out at the very bottom of the container.

4. Brine Shrimp Eggs (Cysts)

There are several different brands of brine shrimp eggs available. For the most part any brand that advertises a high hatch rate (80-90%) will work. The San Francisco Bay brand is popular and a good choice if you are just trying to hatch them for the first time. However, its more economical to buy a large container, like this one.

Brine Shrimp Eggs
Brine Shrimp Eggs

Hatching

Once you have all the materials, you can set up your hatchery and mix up the water, salt, and brine shrimp cysts. There are many different DIY brine shrimp hatchery designs out there. This one by Solid Gold Aquatics is a good beginner tutorial.

In my experience you don't need to add anything to the water besides salt. This includes dechlorinator. The cysts are completely encapsulated and chlorine in normal tap water concentrations shouldn't affect your hatch rate.

The optimal temperature for hatching is 77-80F. Since brine shrimp are attracted to light sources, you can use a lamp with a CFL or incandescent bulb to keep the solution warm, or submerge the bottle in an aquarium that is already at a nice warm temperature. I have found that temperature is more important than constant light for high hatch rates.

Hatched Baby Brine Ready to Harvest
Hatched Baby Brine Ready to Harvest

Harvesting Brine Shrimp

When you are ready to harvest your newly hatched brine shrimp, you should remove the air line and allow the solution to settle for 5-10 minutes. The unhatched cysts will sink to the bottom of the container, and the empty shells will float to the surface. This will leave the live baby brine shrimp swimming in the middle of the solution. Then use a pipette or turkey baster to suck up the wriggling orange cloud.

At this point you can squirt the salty brine shrimp solution directly into your aquarium, but it is better to strain the shrimp out of the salt water using a coffee filter first. You can use either a fine metal mesh or a paper filter for this purpose.

Straining Brine Shrimp
Straining Brine Shrimp

Once you have strained the shrimp into a filter, you can transfer them to some dechlorinated tap water or aged aquarium water before feeding them to your fish. Any leftover baby brine shrimp can be frozen into cubes and fed over the next few days.

Using a Pipette to Suck up Baby Brine
Using a Pipette to Suck up Baby Brine Shrimp

The video below shows live baby brine shrimp being fed to my celestial pearl danio tank. You can see just how quickly the fish devour them.