Backyard Aquaponics
A place to discuss aquaponics

i'd guess that the high PH is due to the algae, as has been said, measure PH early in the morning (best just before sunrise)

everyones got it coverd. reduce or stop feeding, keep the shade on the fishtank.


keep us posted

I was always under the impression that if you nitrate readings then you don't have enough plants. We tested Faye's system on her open day after a tonne of fish food going in for the trout and there were ZERO nitrates.

I would imagine that for greater efficiency you would want to absorb the nitrate as fast as it is being produced.

...ahh grasshopper - you will see

Tim i must be a freak (shut up, VB) its all really clear to me.

I dont mind explaining it again though.

lets use arbitrary figures;


initial nitrates =0
fish nitrate production = 10/day
initial plant nitrate requirement =0/day
net change in nitrate =+10ppm/day

DAY 7

initial nitrates=70ppm
fish nitrate production = 10ppm/day
plant nitrate requirement / uptake = 20ppm/day

net change in nitrates = -10ppm/day

DAY 13

initial nitrates = 10ppm
fish nitrate production = 30ppm/day (we've increased feeding here)
plant nitrate uptake = 30ppm/day (lots of vegative growth to support)

net nitrate change = 0ppm per day

nitrates will remain static at 10ppm



I hope this progression makes it all clear.

its all about net changes and equilibrium
obviously is simplified..............for simplicity

you can have the equilibrium point at any nitrate ppm, its just hard at zero because you dont know if the plants are "starving" for nitrates, ie a net -ve change.
In real life the nitrates will fluctuate up and down with the plant growth (given a constant feed regime (which is not going to happen becasue as the fish grow you feed more)

But if you had plants in there from day one... then potentially you have 0 nitrates from the beginning. It is very possible to have 0 nitrates if the plants are absorbing nitrate faster than it is produced..... I don't see a problem with that. Plants grow, they absorb nitrate, nitrogen cycle creates nitrates at different rates too.

So therefore back the original problem.... If I fed more food all of a sudden, without adding more plants, the large spike in excess nitrates and the spell of hot days here in Perth, it would explain the algal bloom.

Just like when you have a heavy down pour that causes run off from farms, followed by a few days of sun also creates an algal bloom.

no problem except that if they are absorbing quicker than it is being produced then they wont be growing at their absolute max capability.

which there is also nothing wrong with!

if you goal is to keep nitrates as close to zero as possible than go for it, steve and ange often had zero nitrates with great growth in their system.

Huh ha! Who's the grasshopper now VB? Hehe.....

You will indeed see grasshopper, I will count on that. Now all jokes aside, it can prove quite difficult and costly to have sufficient grow-beds in play to get the amount of plant growth needed to remove all the nitrates produced by the amount of fish that many of us do/will end up keeping. As the system matures, there will also be nitrogen produced by the significant amounts of plant matter rotting down in the medium (and/or being processed by the earthworms as well).

I have a very low density of fish in my system now - having eaten many of them, and some really large fruit and leaf producing plants, yet my nitrate levels are still 80. This is with me only feeding the fish every couple of days also (a deliberate measure to try and cut down some of the fat supplies, because I am going to eat the fish soon).

FOr most of the time that I have run my system I have had nitrates somewhere between 80 and 160, regardless of how much I feed or the density of plant life in the system at the time. Applying Steve's simplified example, you would think this impossible. But this is why steve is calling it a simplistic example. The reality is that there are many other things in play here - not the least of which is the anoxic environment that will inevitably occur in bits of the grow-beds (particularly mature gravel ones) and the constant flood drain action. Both these factors will result in off gassing of nitrate. I believe that my system in it's current form reaches an equilibrium for nitrate not from feeding or plant growth rates, but rather through off gassing of nitrates together, of course, with plant uptake.

My grasshopper comments are a little wager that you too will end up with high nitrate levels one day unless:

1. You have much more self control than most of us; or
2. You have much more money than most of us and can operate an excess of grow-beds.

:-)

VB likes his wagers.....................

i only got out of my last one because of a nifty little clause i added in

Am not actually looking for a bet here - was talking figuratively (sp?).

As requsted I took pH readings today.
This morning at sunrise pH 7.4-7.8 24°C
this evening towards sunset pH back up to around 8.8 27°C

Yesterday I did remove some of the water and top up with more rainwater from my tank. We had both AP tanks covered all day with 80% shadecloth - don't have any opaque covers. I've increased the pump run time for most of the day's cycles (to 30 min per hour)

I can't see the bottom of the tank. I trawled the bottom with a net as best I could to see if any food had sunk - all I found was s dead fish and this evening we found a floating fish. I haven't seen any obvious signs of disease on the fish (not that i know much about fish)

I woudl say the evening pH is slightly less than yesterday and taken a few hours later in the day.

Presumably it is wait & see time

I had been planning to add shell grit to the tank - not sure if now is the time to do this

Definitely not..... you want the pH to head in the opposite direction.

looks like the algae is creating the ph swing. early morning is when the CO2 will be the highest hence the lower ph.

No point with the shell grit at this stage as you ph LOW is at the level you want anyways.

give the 80% shade cloth a week or so.

the PH 8.8 is going to be locking out nutes quite a bit, explaining the plant problems.

DO NOT try and adjust ph as it will just bounce all over the shop