Backyard Aquaponics
A place to discuss aquaponics

I've got a new setup in my greenhouse. My tank is 110 gallon plastic horse trough (so I have maybe 85 gallons in the tank), I have a submersible pump to cycle water from the fish tank into my grow beds(clay pebbles) that drain back into the fish tank and I have two air stones. I started about one month ago with filling the system with well water and started cycling. About 10 days later, I added 42 Rocky Mountain White tilapia (3"-5") to the system. The plants in the grow beds have germinated and growing and the fish are doing ok, but this last week, I have one fish dead about every other day for a total now of four dead fish lying on the bottom of the tank. My water pH is 6.5 and water temp varies each day from a low at night of maybe 65 degrees F to a high of about 80 degrees F in the daytime. The water is slightly mirky, but clear enough that I can see the fish on the bottom of the tank. Also, there is a slight partial film of green algae? growing on the surface of the water. I feed once per day, usually in the afternoon, and it amounts to about 1/4 cup of food at which time they come up and hit at the food. Up until last week, I did notice that some of the food not eaten settled to the bottom of the tank. As of this week, I don't see food on the bottom of the tank.
Any insight into why I'm loosing these fish periodically would be very helpful. Also, I am going today to get some test kits and need to know what I should get. Thanks.

Welcome to the forum mtjag.

I believe Tilapia are a fairly tough fish but I'm guessing you're overstocked and probably overfeeding too. Or maybe the system hasn't fully cycled. And I assume you've removed the dead fish.

Let us know a bit more about your system including:

volume of your growbeds - without some other form of filtering, you should have at least 25 L of wet media for each fish you plan to grow to plate/pan size.

Are you getting all your system's water through your growbed about once an hour?

What's your ammonia, nitrite and nitrate (though the latter is unlikely to kill your fish)? Buy a test kit which will also include a ph test. The ammonia and the nitrate are highly toxic to fish. Most of us in Australia use the API Freshwater master kit... easily bought online or at a pet store. Suggest you stop feeding the fish and consider changing some of your system water until you've done those tests.

+1

Definitely sounds like overstocking problems and your system may not be fully cycled yet either.

Thanks much for the insight. A bit more information combined with what you said, as well as scotty435 indicated, pertaining to the amount of fish and cycling of the water. About 10 days ago, it started getting pretty cold here at night, so I turned off the cycling of the water through the night to keep the water temperature up. I have inflow heat running under the tank and that water temp stays pretty constant above 65 degrees, but the temperature of the greenhouse will drop down to 40 degrees on cold nights. So, I was thinking it made more sense not to cycle water through the 40 degree greenhouse to keep the water temp up. Clearly, that was not a good decision. I've lost two more fish this morning, bringing my mortality rate up to 6 total, so now I should have about 38 tilapia in my tank. Today, I brought the water level up in my tank to maximum by adding another 25 gallons so I should be right about 105 gallons now. I also added a filter system that will help partially filter out the nitrites and nitrates and I've set my cycling to run for 15 minutes at 45 minutes interval throughout the night and day. Finally, I will not feed for the next three days. Please let me know your thoughts. Thanks again for the help. BTW, I removed all dead fish the day I find them.

Hiya mtjag, I would imagine it would be better to run your system constant flow while it is still cycling with the fish to build your bacteria colony as fast as possible and to keep exchanging your ft water.

Ok will do. That is what I needed to hear. Thanks much and I will report back.

What skeggly said... although you'll have to work out the best balance between temperature control issues and good water turnover so most efficient biofiltration.

Your filter - though not sure what sort it is - may help in the long run but note that it's the ammonia and nitrites that are likely killing your fish.Suggest getting a test kit should be a priority.

High levels of nitrates (plant food) are said to be bad for plants and fish - though mine have been off the charts until recently with no obvious problems. It's unlikely to be the thing killing your fish right now. But, unless your filter works most effectively as a solids filter as opposed to a biological filter, if you don't have enough plants growing in the system, the nitrates do tend to creep up and up.

You might save some fish by doing a change of a significant amount of your system water to try to get nitrite and ammonia down quickly. I haven't done this myself but think that people with access to water without chlorine sometimes change as much as 30% of their system water at a time. Do a search on here about ways to dechlorinate water if needed... noting that most advice is against using chemical means of dechlorination.

Considering the small size of the plants I have now, it would make sense to go the route of exchanging the water with well water (no chlorine). How frequently should I do this...every day, two days, three days?

I suppose you could do it daily for a while... but that's probably not sustainable. In the end though, you'll know when and if you need to do it by testing for ammonia and nitrites.

Just thinking if I can takeout 10 gallons a day and put in 10 gallons a day for the next couple of weeks, it might give the plants time to really start filtering the water better. (That may need to be moved up to 20 gallons a day)

The filter system I put on today is for a 60 gallon tank, so it is undersized by about 40 gallons based on the roughly 105 gallons of water I have in the tank. So, while it is advertised to take out the nitrates and nitrites, it is less than what I actually need but hopefully will stand in the gap until I can either get the plants larger or get another larger filter.