Aquaponic Gardening

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Hi there, 

Sorry, I'm really new to aquaponics. I am running an aquaponics system with the fish in a cut open IBC bin with a grow bed above that filled with gravel. I set it all up about 2 months ago, gave it about a month to get settled and then introduced 5 comet goldfish. The goldfish seemed fine but they were very inactive and werent eating much and I figured it was because the water was too cold (the system is outdoors). I then put a heater in and got the water temperature up to around 15 degrees celsius, and saw immediate improvement. The fish suddenly started eating. 

A couple of weeks later though, they became very dormant again and didn't eat much and then suddenly one died. I panicked a little bit and did 3 water changes of about 20% of the water on 3 consecutive days. With each water change I also added a product called aquazyme on the advice of the local fish shop. I might have overdone that a bit, I'm not exactly sure what the dangers are of putting too much of that in the water. 

Anyway, then a few days later another fish died. I took a closer look and it seemed like there might have been some dark spots on the fish but I really dont know much about this stuff so it could have just been natural discolouration following its death or possibly even just my mind playing tricks on me. See photos. 

I then tested my water and found that everything looked fine, except maybe the pH level was a bit high (seems around 8.5 - 9). 

I didnt really know what to do about this so I left it and then the next day found another fish floating. This time I noticed this white sort of mucus type stuff around the floating fish's body and also saw a similar type of thing on one of the other fish in the water that was still alive but not looking well. 

Does anyone know if this white stuff is an indication of what is killing my fish and whether it is related to the high pH level and what I can do about it? 

I should mention that at the moment there is nothing growing in grow bed, though the water is still being pumped up into the grow bed and draining out into the fish tank. I'm not sure if that is of any relevance but just thought I should give as many details as possible. 

I also fairly recently put some live plants in the water which I obtained from the local fish shop. 

Any help will be greatly appreciated. 


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Hi Pall - your water is a bit alkaline - do check your media by dropping a few bits in to a glass of vinniger - if it fizz change your media. Also check your water source pH. Gold fish thrive in pH 7.0 - 7.5. Adding stuff used for aquariums could kiĺl off your good bacteria. As it was cold your system most probely only started to cycle properly once you added heat. Plants prefer a bit lower pH - so 6.5-7.5 should keep all happy. AP systems tend to naturaly lower pH over time. Maybe add some plants and earthworms to your growbeds to consume nitrates. I've started my system fishless - seasol in the water and seedlings in the growbed. only added fish month or so later

Thanks Pieter,

I will check the media as you advised, thanks.

What action can I take to reduce my pH level in the mean time?

The water source (tap water) is around pH 7.0.

Hi Pall - if you're in Pta - the chance good that you've got dolomite gravel - CaMg(CO3)2 which is probably the problem - try getting granitic gravel from Brits/Rustenburg. Unfortunately dolomite does not always fizz noticable when tested with viniger.

Seems like you'll need to start again then with new water and media. You can use NITROSOL to start your system fishless - just check that it is the fish and bee friendly variety. It will get the bacteria going. You can also start with seedlings. You can introduce fish in a month or so time - if AP measurements in agreement.

All the best!

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