While fish are still in the concrete pond, it is not advisable to drain the water completely in an attempt to change their water. It is good to reduce the water in the pond to a level and then top it with fresh water. So, washing the pond may not be necessary in the course of raising the fish.
It is advisable to be done after cropping that is after harvesting your fishes. However, if in the course of raising the fish, the pond becomes extremely slippery, then you can wash the pond with clean water and this is better done alongside with sorting of the fishes so that the fishes are not in the pond while washing the pond.
Concrete fish tanks (because of their labor and materials costs) usually cost as much or more than solid fiberglass tanks do. However, if you have free gravel and labor, they can be really cheap. If you don’t, they can often be more expensive than solid fiberglass tanks.
Think twice before using concrete structures; they will still be here 1,000 years from now because they are difficult and expensive to remove. If you do use concrete tanks or troughs, make SURE you get them in the right place, and have any plumbing fittings installed in them before you pour or apply the concrete.
Here’s the best way to neutralize your concrete fish tank:
After your concrete has cured (if you don’t know what this means, you have no business building concrete tanks anyway) plug the drain in your tank, and apply the acid directly to the concrete using a brush with plastic bristles, wearing rubber gloves, protective face shield, cartridge respirator, high rubber boots, and long-sleeved protective clothing.
You need a hose with a squirt handle on it right at the top of the tank so you can hose yourself off and dilute the acid in case you accidentally get some on your clothes or skin!
The acid is known as muriatic acid, and is sold in hardware stores and building supply stores; it’s just another name for hydrochloric acid! After the acid has set on the concrete for an hour or so, rinse it off, but DON’T LET IT GO DOWN THE DRAIN!
Leaving the acid and rinse water in the tank, now fill the tank to the top with the water (remember, you plugged your drain first?), and let it sit and soak for a couple of days. The diluted acid in the water will now have a chance to soak into and completely neutralize the highly basic new concrete.
Now drain the tank water off to a location where the acidic water cannot harm animals, plants, or people. When it is empty, rinse the inside of the tank well with a hose, letting this water go down the drain also. An ideal safe place is into an existing cesspool or septic system.
Now, check the pH of the water supply you use to fill your tank, then refill the tank to the top with new water and let sit for two days. After two days, check the tank water pH and compare to the pH reading you took of your water supply two days ago.
If the supply water pH was 7.2, and after two days in the tank it is now 8.5 or higher, you need to repeat this process with the acid wash, sit and soak AGAIN because your concrete is still bleeding off alkali (base) into the water. If your tank water pH reads between 6 and 8, you’re fine and can start your aquaponics system.
The only exception to this might be when the supply water you started with is VERY basic, i.e. 8.5 or so. In this case, if you had pH 8.5 water, and after two days in the tank it was only 8.6 or 8.7, it’s probably OK to start your system. This is an area we don’t have a good solution for yet: how do you adjust your system if your pH is high? (See System Startup and Water Quality sections for more information on pH).
Important! If you have trouble getting the pH under control in your concrete fish tank for some reason, you can do what some of our students have done: either line the tank with a vinyl liner, or smear a thick layer of household paraffin (wax) on the inside of the tank.
Both of these methods leave the inside of the tank a neutral surface that is safe for the fish. We’ve never gotten a concrete tank certified, though. To make sure your ability to get organic certification is not compromised, you should check with your proposed certification agency before committing yourself to concrete tanks.
WARNING! Do NOT try to bring high pH caused by having a poorly neutralized concrete fish tank in your system down by using citric acid! Citric acid is an organic HERBICIDE, and will kill your plants roots. They all turn black, then the plants all die.
7 Tips to Keep Pond Water Clean
1. Maintain a healthy fish population
If you have more than 10” of fish for every 100 gallons of water, your pond is likely over-populated. Excessive fish waste can cause an imbalance in pond water. Consider finding some of them a new home. Many pond retailers and contractors will accept your fish.
2. Don’t over-feed your fish
When you feed fish more than they can eat, the uneaten food is left to decay in the pond. Be careful not to feed your fish more than once per day, and no more than they can eat in 2 to 3 minutes. Choose a quality fish food – preferably one that floats as opposed to sinking to the bottom of the pond if left uneaten.
3. Create a proper balance of plants
At season’s peak, you should have 40% to 60% of the surface area of your pond either covered or shaded by plants. Too many plants can cause oxygen deficiencies at night due to the photosynthetic process, when the plants take in oxygen and give off carbon dioxide. Your fish need the oxygen to survive (see tip #7).
4. Choose the right size pump for your pond
You should be circulating the entire pond’s water volume a minimum of once every hour. Make sure your pump’s flow isn’t restricted by debris in the skimmer or biological filter, and be careful not to pump water higher than it was intended. Every pump has its flow limitations.
5. Clean debris from pond before it has a chance to decay
Your pond skimmer will remove most of the debris from the surface of your pond, but you can also use a pond net to skim leaves and small sticks before they have a chance to descend to the pond’s bottom where they’ll decay. Decaying debris, combined with fish waste and leftover fish food, can cause ammonia levels to spike in your pond.
Ammonia can be harmful to your fish and should be addressed right away. If you see your fish jumping out of the water, you likely have an ammonia spike which can happen after adding an algae treatment. You can purchase an ammonia test kit at your local pet and aquarium store and if you find the levels are high, simply treat your pond water with Ammonia Neutralizer.
Beneficial microbes such as Aquascape Beneficial Bacteria helps keep your pond water healthy and clean for your finned friends. Better yet, install an Automatic Dosing System to electronically dispense beneficial bacteria and other treatments to your pond to help with breaking down debris and maintaining a proper nitrogen cycle.
6. Choose proper filtration for your pond
Just like your pond pump, your pond’s filter should match the size of your water garden. Most pond filters are based on ideal circumstances, and if you exceed those, your filter becomes less effective. Always up-size your filter so that it can handle more than the capacity of your pond and remember to clean your filter according to instructions.
There are two types of filters in an Aquascape ecosystem pond. A mechanical filter, also known as the skimmer, removes surface debris from your pond water such as leaves and small sticks. The biological filter, or BioFalls filter, is positioned to create the beginning of the waterfall in your pond.
This filter uses bacteria to break down pond wastes, converting them into less harmful compounds that can be absorbed as fertilizer by your aquatic plants.
7. Keep your pond cool during the dog days of summer
When pond water exceeds 75º Fahrenheit, it has a difficult time retaining acceptable levels of dissolved oxygen, which is critical for the health of your fish. This is why it’s important to have the surface of your pond shaded by aquatic plants (see tip #3) – to help keep pond water cool. Fish need oxygen to survive. If you see them at the pond’s surface gasping for air, add an aerator to help them during times of extreme heat.
Here are some amazing catfish farming books that will guide you further: