Using Tap Water In Aquaponics

Fish tank half filled. I let the systems run for week to let the chlorine in tap water evaporate before introducing fish and bacteria. #aquaponics #growyourown #permaculture #urbanfarming #landscaping #fishfarm #aquaculture

The easiest way to fill or top up an aquaponics system is by using ordinary tap water. Here is what you need to know about using tap water in an aquaponics system.

The chlorine present in tap water is potentially harmful to your fish and the bacteria colonies living in your growbed. There are methods of dechlorination including, letting the water sit for a few days to allow the chlorine to evaporate or to add dechlorinate to the water.

I personally like to keep things as natural as possible so dechlorinate is out of the question for me.

When filling up the system for the first time you’ll need to allow at least 72 hours for the chlorine to evaporate from the system before adding fish or seeding with bacteria.  A week would be better. Run the pumps during this time to aid in the evaporation of the chlorine.

During normal operation, your system will lose water due to evaporation with the rate of evaporation depends on the time of year, weather conditions, or whether the tank has cover. You can let the water level drop a quarter of the volume of the fish tank before you need to top it up.  If you ever need to top up more than half of the tank you must do it in batches over a couple of days to a week.

Tap water is suitable to be used right from the tap if you need to top up the level in your fish tank. However, only ever add tap water directly to the fish tank.

Never apply tap water to the vegetable garden filter as the chlorine in the tap water can kill off bacteria colonies.

As long as you don’t top up any more than a quarter of the volume of the tank over 3-4 days and fill up only via the fish tank then the systems and fish will be fine

However it is worth mentioning that by adding new water to your system you are likely adding water of a different ph to the water in your system. If you are topping up a quarter or more of the volume of your system you are likely to cause a ph spike in your system.

The ph of the water is important for many reasons.

All fish have a preferred ph range and ph can affect fish health, mainly due to its affect on increasing ammonia more toxic at higher ph.

Ph has a huge impact on the plants, more specifically, the ability of the plants to take nutrients from the water. At higher ph, the plants become very poor at being able to extract the nutrients in the system. Your system might be bursting with nutrients; however at a high ph the plants may be unable to use them!

You are looking for a ph of around 7.0 as optimum for the plants (some species prefer higher or lower ph however 7.0 is good concession for both plants and fish). The process of converting fish waste to plant food will naturally lower the ph in mature systems, however in early establishment the system does not have enough bacteria to make a difference to ph.

Before you top up your fish tank, take a ph water test reading  – after your top up take the reading again.

If the reading is a full number up or down on the scale, fill a bucket of water from the water source (hose), let it sit for a day and take a ph test. This way you will be aware of the ph of the water you are introducing into the system and make adjustments if necessary (another post about this coming soon!).


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Written by Suburban Farmer

Hi, I am Mike the Suburban Farmer. I have been practising backyard self-sufficiency for 15 years and aim to inspire you to look at your backyard in a new way, and to enjoy the many rewards from growing your own.