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I am concerned about the amount suspended solids in my system. Even at night with a flashlight, it is not possible to see the bottom of the IBC fish tank. The water is clouded with what looks like dust, could be fish poo. I don't know. The system is now 5 months old.

Here are the details of our system:

The fish tank is a 275 gal IBC, in which I keep a constant height of about 260 gallons.

The grow beds consist of 4 IBC halves filled with 3/4" gravel. They are constantly flooded directly from the FT and drained through bell siphons in +/- 15 minute cycles. The gravel beds drain into a sump tank and from there the water drains into a 4'x20' DWC.

Water from the DWC in pumped back up into the FT constantly at +/- 600 gph, allowing for a water exchange of a little better that 2x per hour.

Aeration is supplied through an inline Venturi aerator in the return plumbing to the FT. In addition there are four 4" air stones in the DWC, one of which is located next to the inlet to the pond pump supplying the FT.

The water tests yesterday were as follows: pH 6, Ammonia .5-1 ppm, NO2 was 0 and NO3 was 40-80 ppm using an API test kit.

Now to the fish. There are, or were, 24 channel cats in the tank. These fish were fingerlings 5 months ago. I took all the fish out of the FT in a futile attempt to clean the tank. The tank was not the problem, it was the water. I did not realize our 5 month old fish were so large. So, I harvested the 6 largest fish and we had a fish fry. Now 48 hours later, minus my biggest poo-producers, the water may be clearing up.

Any suggestions? Thanks!

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Replies to This Discussion

Do you have a bio filter with worms? If not it would help.

A amber tint is normal. It means your system is mature.

Ok, you are fairly heavily stocked if you were growing out 24 channel catfish in that IBC.

But the biggest issue I see, is that your pH may be too low.  If you are testing the pH with the API master test kit and it says 6.0.  Then it could be way below that!!!!!!  You have no way of knowing because the test only reads down to 6.0

To those using the API test kit to monitor the pH of their systems, I recommend keeping the pH up about 6.5 and testing often.  So that you can catch it before it gets to 6 or below.

The fact that you are seeing ammonia levels between .5 and 1 ppm tells me that your pH may have crashed a bit and the ammonia is starting to spike.  Time to stop feeding till the ammonia drops and bring the pH up a little but do it carefully since ammonia becomes more toxic as pH rises.

low pH and the ammonia spiking and over feeding can all contribute to difficulty seeing the bottom of the tank.

Them catfish grow fast in warm weather don't they.

Good point, TCLynx. My, current, favorite way to test pH is to do a titration, but that may be a bit complicated for this situation. Also, I believe toxicity of NH4/NH3 goes up with temperature, so depending on where you live, it is imperative to get the ammonia/ammonium down. 

Hi John,

Wow! what a flowrate! The fine solids probably don't have time to settle out with the filtration offered by 3/4" gravel. You can replace some of the 3/4 with pea gravel, adding to your mechanical filtration, and i believe, helping also with nitrification as well. Or you can place a net filter before your raft as this amount of fine particles can affect roots in the DWC. If you want to slow the flowrates down a bit you can use a bypass line from the pump to FT, or a loop with valve back to the pump itself.

From your readings though, I think it best to deal with the PH issue before you focus on the other lesser concerns.

@Eric... "I believe toxicity of NH4/NH3 goes up with temperature, so depending on where you live, it is imperative to get the ammonia/ammonium down"

Ammonia toxicity has inter-relationships between temperature AND pH... and generally yes... the toxicity increases with temperature increase... that is the "safe" level of ammonia is lower as temperature increases...

But it is probably more importantly related to pH...

I was going to include a chart...but don't seem to be able... (or edit, or other things)... strange...

You probably have some better info and charts Rupe, but this should at least be in the ballpark eh?

 To use the chart below, in order to determine the amount of the toxic (un-ionized) form of ammonia (NH3) present in a given amount of total do the following:

1- Using the appropriate water test kit, determine the amount of total ammonia ion in your systems water
2- Determine the temperature and pH of the water.
3- Refer to the chart (below) and locate the numerical value that corresponds to the temperature and pH of your water.
4- Multiply this number by the reading for total ammonia (from step 1). The result is the amount of toxic un-ionized ammonia (in mg/L) in the aquarium or pond.

 Foe example...The pH is 7.0, the temperature is 18° C and the total ammonia reading is 0.8 mg/L. Locate the appropriate numerical value (in this example it is .0034). Multiply 0.8 times .0034; the result is .00272. This means that there is about .003 mg/L of NH3 in this example.

Let us know if this jives with the way you do it Rupert

John is it a 600 gph pump?  Or is 600 gph the actual amount of water flowing through the fish tank?

Either way, 600 gph isn't that outrageous for a250-300 gallon fish tank really, especially if there is no other form of aeration to the fish tank other than the water flowing in through a venturi.  If it is actually that high a flow rate through the fish tank, I think that might be the only reason that your fish have survived thus far as their size got a bit big for the small tank and their numbers.
  The high flow rate and the big fish stirring it up mean that any solids still in the fish tank tend to be flowing around and clouding the water instead of settling down on the bottom the way they might with only a few small fish.

The big gravel might let some particles through but there are plenty of systems out there using the bigger media and with a  sump and 20' long raft bed, I expect most of solids that make it out of the fish tank are settling out in there.

If the fish tank is having a lot of suspended solids you might need to figure out how to adjust the flows and drain on the fish tank to get the solids out since I expect the problem might be that they are just having difficulty finding their way out of the fish tank and you were probably over stocked and over feeding for the flow patterns and fish tank volume.

Did you happen to weigh any of those fish you harvested?  They look pretty good size for only having them 5 months.  How big were the fingerlings you got and what have you been feeding them.

By the way, GOOD JOB to be eating fish out of an aquaponics system after only having it running for 5 months, most people have to wait more like a year for that.

Let us know if this jives with the way you do it Rupert


Ah have the edit functions back now... kind of Vlad... (it's the more correct way)...

But most people use a test kit that meausres Total Ammonia Nitrogen... TAN...

So more like this chart... (can't find the fahrenheit version sorry)


Cool. Thanks Rupert. Your way seems easier.

@TCLynx The pond pump is actually moving more that 600gph, but I am bypassing the excess back into the DWC. That is another good source of aeration in addition to the Venturi and the air stones. The pump is a PondMaster 9.5.

I did not get the weight of the harvest, but they were all at or near 12 inches. They were 3-5" fingerlings five months ago and we feed them Southern States Aqua Specialty.

It's been 3 days since taking the 6 big poo-producers from the FT and I can see a definite improvement. The water is clearing up.

Now I need to work on the low pH. Looks like I can use baking soda (3.5 cups in 10 gal. of water for my 850 gallon system, added slowly over the course of the day).

don't use baking soda if you can avoid it.  It adds way too much sodium to the water that the plants don't appreciate that much.

You want to make sure you don't raise the pH more than about 0.1-0.2 per day.

Appropriate things of raising the pH in aquaponics include

hydrated lime (calcium hydroxide) beware this is very strong so you might want to do some testing with your system water and a bucket so you can figure out for example how much is needed to bring the water in a 5 gallon bucket up to say 6.2 or just start tinting it the slightest bit green.
  Warning, since you don't actually know how low your pH is, getting to just above 6 may actually be moving your pH far more than 0.2

Anyway, hydrated lime is available at pretty much any hardware store.

The other really strong pH elevator that we sometimes use in Aquaponics is potassium Hydroxide (old fashion potash lye!)

It is also very strong.  You need to handle both hydroxides with extreme care and safety precautions.

If you are not comfortable with hydroxides.  The other option is to raise the pH with carbonates and bi-carbonates.  The ones we usually use are calcium carbonate (lime or shells) and potassium bicarbonate (found at wine making and brewing supply stores)  They (especially the calcium carbonate) are gentler and slower acting which can be problematic since people have a tendency to add too much when they don't work quickly enough.  So for your situation, you probably shouldn't use this method until you get the pH up to a readable level and then you can use a small amount to buffer the system.  Keep in mind that the carbonates and bi-carbonates buffer the pH up and if you add too much you loose control of the pH and it will be hard to bring it back down.  Many people will use shells in a mesh bag hung in the system so that they can remove them if the pH is too high.

Another option (and this will depend on what your source water is) would be to top up heavily or do a partial water change.

What is your tap water pH after you have let it outgass or bubble for a day?  As in, if you use well water and you have hard water, doing a small water change or topping up heavily could easily bring your pH back up and add a fair bit of calcium carbonate or bicarbonate to your system.  (That is the case with my well water, I generally don't want to add any sort of calcium buffer to my system beyond what my well water provides because I then wind up with way too much calcium and not enough potassium.  So I generally don't bother with the calcium hydroxide or calcium carbonate and I just use potassium bicarbonate to bring my pH up when I have enough rain water that the system pH needs buffering.  When I run low on rain water and have to use well water, my system gets plenty of calcium.)


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