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PostPosted: Jun 24th, '19, 05:18 
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Hi everyone, I'm pretty new to Aquaponics, and have started two of my own systems here in Zambia, Africa.

The short of it is I'm worried about how much algae is in my system and whether I need to slow down my fish feeds.

***Some background info:
Both of my systems are circulating about 15 000 litres (3962 gallons) of water each. Each system also has two big fish tanks that hold about 4500 litres each. Each system has 12 grow beds, either filled with stone or rafts getting ready for lettuce. Currently 5 beds have been planted in one system, and three have been planted in the other. I have added tilapia fingerlings into each system. 400 3cm fingerlings into one system and 200 8cm fingerlings into the other in order to cycle my systems using fish. This was by recommendation from someone who knows quite a bit about aquaponics with many years of experience. Since these introductions, I have lost around 150 of the smaller fingerlings and 100 of the bigger ones supposedly to a bacterial infection which I treated with potassium permanganate under advice. Since then the deaths have dropped to around 2-4 a day. Our water temp is not ideal as we are currently in our winter month here, so it is sitting at 19 degrees celcius on average.***

My worry is that the algae in my system is growing so quickly that I can't really see the fish. I have read on the forum that 'feeding the fish must be kept to a strict minimum for the first 2 months. No more than one tablespoon of feed, per day, per 500L of media. If you get an algal bloom, stop feeding until the algae clears. After 2 months you can start increasing feed levels slowly because your bacteria would have been established.'

I was advised to feed the smaller fingerlings 5 times a day, which is amounting to around 2 table spoons a day, and then the bigger fish to feed three times a day, with about 25g of 2mm fish feed each feeding. Should I stop since I can't really see into the tanks? the algae is growing quite rapidly since my systems are in a white tunnel. I have put tarpaulins above the tanks to try and prevent the algae growth, but don't know if this was the best move?

Sorry for the long question, but thought a bit of background info would help...


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PostPosted: Jun 25th, '19, 08:39 
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You really need to do some water tests and see what your parameters are.. Ammonia, nitrites and pH..

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PostPosted: Jun 25th, '19, 10:47 
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...and Nitrate as well.

19C is getting down towards the bottom end of the temp range for tilapia, especially small fingerlings. It's inside their survivable range, for larger fish at least, but is 2 or 3 degrees below the bottom end of their comfortable range, so that won't be helping with fish health.

Algae needs two things... Light and nutrients. You can't remove the nutrients from the water in aquaponic systems, so you have to stop as much light as possible from getting to the water, especially fish tanks and sump tanks etc, but also the sidewalls of grow beds if using opaque material, such as IBC's.

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