Fish Tank Discussion

We can’t say, “this tank is best”, or “that tank is no good“; because this varies widely depending on what is available locally, local labor costs, climate requirements and other criteria. So we give you this tank discussion so you can figure out the pros and cons of each type of tank in your specific situation:

Any or all of the tanks in the system can be, depending on what you have available locally and its cost: 1. Solid fiberglass. 2. Black polyurethane custom-formed plastic tanks. 3. Lined corrugated metal tanks with 20-mil or heavier food-grade vinyl liners. 4. Food-grade vinyl-lined aboveground swimming pools. 5. Exterior plywood with fiberglass skin inside and on the bottom (MUST BE well-preserved on the exterior surfaces with HiBor borate compound wood preservative with 3 coats of oil-based paint over). 6. Properly cured and scrubbed concrete tanks.

(Below) One of the inexpensive, yet durable and movable, corrugated galvanized steel tanks lined with an NSF-certified liner (this means “food-grade) we refer to as “our favorite”.

Our absolute favorites (because we’re basically lazy) are the lined corrugated metal tanks in #3. They are easily movable, reusable, and relatively cheap. Their drawback is that the liner punctures easily. The good news is that the liner repairs easily with a piece of rubber tape, the bad news is you have to get the puncture area dry for the tape to stick, which means taking all the fish and water out and putting them somewhere else for a while. Do not use hypalon, EPDM, or neoprene rubber liners on corrugated metal or swimming pool tanks; the fish will nibble algae off any liner over the corrugations, and will nibble right through this type of soft liner. WARNING: Get food-grade vinyl liner if you are concerned about organic certification, and make sure you get an invoice that states that clearly that you can show your organic inspector.

Here are a couple of sources for these tanks and liners:

Corrugated steel round fish tanks come from Scafco Grain Systems, http://www.scafco.com/grain/products/water-tanks . Tell them you need an open-top tank, not one with a conical steel roof, which you don’t need or want for a fish tank.

For tank liner, order standard sizes AND custom-sized round and rectangular food-grade vinyl liners from DLM Plastics, 1530 Harvard Avenue, Findlay, OH, 45840, 419-424-5250. Get “White NSF-61 PVC”, it is FOOD-GRADE vinyl (the “NSF” on the label means “National Sanitation Foundation”).

WARNING! Do NOT use any galvanized tanks or surfaces in your system with NO liner on them. Zinc (what is used for galvanizing) is toxic to both fish and vegetables. You have no control over how much zinc sloughs off the tank into the water, as this is highly pH and temperature dependent. We have reports of unlined galvanized tanks creating toxic conditions for both fish and vegetables. If you must use an existing galvanized tank that is already in place, and you are unable to procure a food-grade vinyl liner for it, you can dry it out and paint three coats of a good food-grade epoxy paint on the interior to provide a barrier between the tank water and its zinc surface.

Fiberglass tanks may be available in your location. These are great tanks except they tend to be expensive, and are quite difficult to move if they are larger than 10′ diameter because they are not easy to “latch on to” and you can break them during a move if you’re not careful. They usually cost three times as much as lined corrugated metal tanks when new. They’re easy to repair, depending on the size and location(s) of the hole(s) or crack(s), if you have someone who knows how to do auto bodywork or boat fiberglassing. If you find good used ones at a decent price and can move them, grab them, they’re GREAT tanks! But, make sure to read the following warning paragraph, which applies to any kind of plastic tank, including fiberglass tanks!

Polyethylene (plastic) tanks may be available in your location. These are great tanks except they tend to be expensive, and are quite difficult to move if they are larger than 10′ diameter because they are floppy and you can break them during a move if you’re not careful. They can cost twice to three times as much as lined corrugated metal tanks. They’re difficult or impossible to repair, depending on the size and location(s) of the hole(s) or crack(s), unless you have a costly plastic welder and someone who knows how to operate one. If you find good used ones at a decent price and can move them, grab them, they’re great tanks! But, make sure to read the following warning paragraph, which applies to any kind of plastic tank, including fiberglass tanks!

WARNING! Be VERY CAREFUL of USED fiberglass tanks, IBC totes and any Polyethylene tanks! IBC totes are those white plastic tanks that look like cubes with a metal frame around the outside. They’re often used in agricultural operations for spraying pesticides and herbicides, or holding various combinations of chemicals and fertilizers. We’ve run into problems with totes that held propionic acid, a preservative. That one killed all the fish in the student’s system.

A tote that the seller says was used “to hold citrus products” for instance, may also have been used to hold insecticides or herbicides at the same location ” for just a little while”. The polyethylene plastic the totes are made of is somewhat porous and absorbs whatever is contained in the tote, to be released later. If it is toxic, it may kill your fish. There is no way to be absolutely certain a tote hasn’t had anything toxic in it, except buying a brand new one from a manufacturer. Getting a tote from someone you trust who will guarantee it never had anything toxic in it is better than nothing if you can’t find a new one.

Because it’s so huge, we’ve split off the Concrete Tank portion of this post into a separate article titled (amazingly enough!) Concrete Tanks.

We like plywood/epoxy/fiberglass tanks for our commercial aquaponics farm because: they use relatively cheap materials, they are lightweight and movable, and they are easy to customize into special shapes and sizes with internal compartments to get exactly what you want (something that is expensive to do with both concrete and solid fiberglass tanks). We have a tank that cost us $1,200 in materials and two weeks of labor by two people to build. This same tank would have cost $24,000 from a mainland fiberglass company, would have had a 12-16 week lead time, and would have cost another $10,000 in shipping to get it here. We saved $32,000 and got the tank here 10 weeks sooner by building it ourselves.

The problem with these tanks is that you need to learn how to build wooden tanks and fiberglass them yourself; there’s usually not a neighborhood plywood tank builder handy. It’s not hard: you get a great plywood/epoxy/fiberglass tank manual in your DropBox files, in the “Manuals” folder.

Disclaimer and WARNING: These tanks MUST also be fiberglassed on the outside of the bottom; MUST be treated with HiBor borate-based (safe) wood preservative, then painted with three coats of oil-based paint on the exterior, MUST be properly glued, screwed together, and fiberglassed by someone who KNOWS WHAT THEY’RE DOING. If all these guidelines are followed, they are excellent tanks. There’s a sailboat named Tropic Bird on the island of Kauai that I built and launched in 1978 that is still carrying passengers today, which is built in exactly the same manner.