Backyard Aquaponics
A place to discuss aquaponics

TT, just a clarification?

When they say "plants" don't they mean "aquatic plants" ?

Terrestrial plants exchange O2 for CO2 during day light and the reverse at night, but this is to the atmosphere

Aquatic plants do the same but the exchange is via the water.

??

I also agree with Steve. The plants in your growbeds will exchange gases to and from the atmosphere. To a very small extend, water drawn up by the plants would contain o2/co2, but the gases are merely used up or escape.

Unless you have a giant algal bloom the effect of oxygen and carbon dioxide levels due to transpiration would be minimal.

So, the grow bed plants will help with aeration, due to the agitation and disturbance of the water, but not be an issue for night time co2 spikes?

On a similiar thought, would a bunch of plants in a greenhouse increase the amount of oxygen in the greenhouse during the day?

yes on both counts. and co2 night spikes should be proportional to amount of algae in the water.

infact co2 in a CLOSED green house shortly after day break can be an issue i think

interesting fact i read once, something like 70% or more of photosynthesis of CO2 is carried out in the oceans by phytoplankton

So a timed fan to vent the air in the greenhouse in the hours before and after dawn would help with that. And for seperate duckweed tanks, if you stopped the circulation at night, I wonder how long it would take to get the o2 levels back up before starting up the circulation again?

Yea Steve, it was in reference to pond culture, i should have noted that.

i think duck week leaves may actually interface with the air, but i'm not sure.

i know for a feact that azolla does, as its a nitrogen fixer

Ripper night last night, covering off the whole water quality thing.
General issues encompassed in the following activity designed to tease out some whys and wherefors.

Task
Results from a recirc system are shown below. System is stocked with silver perch fingerlings, feeding well, with few mortalities. Explain this given that several water parameters are far from ideal. Discuss.

Table
Parameters Data
pH 5.42
Ammo >1.5ppm
Nitrite 0
Nitrate 0
Carbonate Hardness 10ppm
Hardness 100ppm
CO2 48ppm
Water temp 23.2C
DO 11.86ppm


Our findings included the following suggestions:

pH being so low reduced the toxicity of ammo. (The higher the pH, the higher the toxic effect of ammo.)
pH being so low has meant bio-filter has been knocked out or is "off-line." Nitrifying bacteria need a sweet spot between about pH 7 and 8 in a perfect world.
Gradually increasing carb hardness (sodium bi carb etc) will gradually raise pH and let nitrifying bacteria establish themselves and ultimately reduce ammo.
General hardness fine for this species
High CO2 means perhaps the fish have just been fed, perhaps the reading was taken at dawn, perhaps an algal problem in the tank due to overfeeding etc
Temp-fine DO- really good, just below saturation levels.

We concluded that good DO levels will compensate for a lot of other evils.
Ordinarily Silvers would be happier at a higher pH
Ordinarily they would prefer no ammo in the water
Ordinarily they would require a greater buffer in their water
Ordinarily they would prefer less CO2

However, with such high DO levels, many sins in this system are forgiven. The fish are feeding well, show little sign of stress and mortalities are low.

There are several aquaponic applications here:

We all need airstones, especially if we are not pumping to gbs 24/7
A bigger capacity pump with a tee return to the fish tank is an excellent way of utilizing over capacity of ur pump>more air-good
Silvers will tolerate ammo at high levels at a low pH
Buffer slowly. If u wacked in the sodium bi-carb and buffered to pH 8 straight away b4 ur nitrifying bacteria re-established, u will kill ur fish.
High CO2 levels are linked to low pH. Back off on the feed, raise ur pH slowly, let the bacteria do their job
Maintain ideal temps
DO is king
Again, a lot of this is basic stuff to people coming from the aquarium side of things. People like me tho, with nfi, don't know this stuff. Hope it helps some out there.

Very good analysis.

You mention that the fish are feeding well. That's great, but stop feeding them entirely while you get your ammonia and pH straightened out.

Also if you use potassium bicarbonate instead of sodium bicarbonate, it will act similarly for buffering and raising pH, but it will also help nourish the plants. The sodium won't help the plants any; I haven't decided if it would actually hurt them. I got potassium bicarb on eBay as a buffer for wine-making.

another possibility for those results. The recirc system has no biofilter (yep i have seen one ) and the water is sourced from a spring which flows out of a peat bog (seen this too, not both the same place, as the farm using the peat bog springwater doesn't recirculate ANY water)

Thanks for the hint on the potassium bicarb Janet. At Tafe they are coming at it from purely an aquaculture point of view, with no thought to plant nutes. It was a simple case study to incorporate a bit of what we had learnt and yes the obvious thing to do given those results is to stop feeding and buffer slowly. It got me thinking about the low pH in EBs system. Perhaps he just has a lowish stocking rate and really high DO, so fish that would otherwise stress are fine. Thoughts?

Be nice not to have to worry about how much water is used eh Daniel. Rain is becoming less predictable and less frequent.We should all have as many large water tanks as we can fit/afford, so when it does rain, it don't just go down the drain. (Preaching to the converted i know.)

No idea how anyone runs with a very low pH -except- with low stocking rates and good DO. After seeing the dramatic change in the ease of maintaining water quality with neutral pH, I'm going to work hard on my pH.

I must say after adding shellgrit, it has made my nitrite bacteria much happier these past 6 weeks or so. Early on, we were in the mid-low 6s pH wise and had consistently high nitrite readings. Now at pH7.5, we are feeding more heavily but nitrite has dropped to almost zip.

I have put my fish losses down to H2S. My pump sits above the tank floor. I was scrubbing walls,base etc weekly and then running my spa filter for an hour. This reduced any possible build up of anaerobic zones. Stopped doing it for a couple of weeks and had regular fish deaths. I initially thought it was the cold, but they had purple gills upon inspection, which is a pointer to H2S. Needless to say, i am back to scrubbing and aerating!

TT how much shellgrit did you add to your system? I have 3kg in my system and it is not doing much..

The course sounds good....i think I might enroll in the next one.

LB