Backyard Aquaponics
A place to discuss aquaponics

Just lay off the feed for a few days and then feed lightly and the nitrates will eventually come down.

Lowest documented level I've been able to find.... is 450ppm... for bluegill....

But 800ppm... is huge... and I'd be concerned...

How are you measuring a reading of 800ppm... of nitrates???

0.5ml of tank water in the 5ml vial with 4.5ml of rain water should give a reading of one tenth of the actual level. The reading I got most closely matched 80ppm, so I make it roughly 800ppm.

Next weekend I will take 5ml of tank water and add it to 45 ml of rainwater, shake and not stir, then take 5mls of that. That should improve the accuracy with measuring out the tank water.

Thanks Charlie, Ryan and Rupert.
Water change is a possibility but we are not on scheme water and all our water falls from the sky or is trucked in. This year we only have 14000 gal so far out of a total storage of 50,000gals. So we are a long way off filling up. Water costs about $140 per truck load of 3000gal (and looking at a $3000+ water bill this year). While the cost of the water for a water change is about $45 (2 X50% water changes) and no big deal I would rather not if I dont have to. I would love to water the plants but at this time of year they dont need watering.

Add more grow beds... and grow more plants...

Hi Marc,

I am on tank water too but I didn't think this year had been too bad, its the end of winter and I have collected 225,000L out of my 320,000L capacity. Is it possible that some of your downpipes are blocked or busted?

Not likely as I keep a close check on all downpipes. All the downpipes connect to a ring main so water can flow both ways. Also check how much has fallen and how much we have collected. Knowing that it makes it easy to ID if there is a leak in the delivery pipes or the kids are having 20min showers!

We had next to no rain in July and this month while OK has not been great.

Apologies for all the imperial values but the one and only measure I have not converted is our rain water - probably a carryover from when I was a kid.

That is a shite load of water storage Simo. You must have a lot of roof area to collect all that.

It seems that the season has not been too bad out your way as you are only 100000l (22,000 gal) short of full. For us it is shaping up to be the driest winter on record - even Perth has had more rain.

Fingers crossed for a big finish

It seems that the season has not been too bad out your way as you are only 100000l (22,000 gal) short of full. For us it is shaping up to be the driest winter on record - even Perth has had more rain.

That is a great solution Rupert but I already have 5 beds, all fully planted. 5 beds is an "overkill" for 28 trout but clearly that is what is needed. I would be interested to see what the nitrates are like in a 5 bed system with 100 trout!!

I don't think so; I think this is an excellent example of how you don't need a massive stock density of fish to achieve abundant supplies of fresh fruit and veges.


I now have a BYAP system with 500L media and it easily "supports" 20 fish, however, the fish are fed moderate amounts and the nitrates have been under control since installation. Having 5 times this i.e. 5 GBs with 100 trout should be just successful, so long as all the other rules regarding volume of water, water turnover, filtration and aeration are similarly scaled up, and the system owner takes charge of the nitrates by controlling the quantity and quality of the feed added to the system; just ask Faye who runs 5 GBs in her system with extraordinary success.

We know you own a water test kit as you've been explaining the 800ppm observations; but how did the nitrates get that high in the first place? When the nitrates went 100+, didn't that set off some alarm bells? 200+? 300+? If you hadn't been doing regular (weekly) monitoring before, it might be a good time to start more frequent observations until you figure out how much feed is required to keep your system in the required balance?


Scott

My trout feeding charts say that you should feed 0.8% body weight per day for fish 500-750gms at water temps between 14 - 18C. Although that fish weighs 750gms I would say it should only be about 600gms if you disregarded the fat. So, taking that into account that makes 4.8gms per fish per day which comes out at 940gms per week for the 28 fish.

Do you feed your marron at 3% gav? Sorry off topic but for my own personal interest... Ive read thats the going rate.

They eat whatever their lucky enough to get. Fish are now my main focus and most of my ponds are now solely devoted to them.

That may be true Bunson if vegies are your priority. Not everyone sees it that way. Many people like me have abundant land to grow vegies so the attraction is to grow fish



You are right Bunson; I have scaled up very well, with 5000l of water nearly 3000 litres of media filtration, aeration that makes the tanks look like spas and running on a 15 min cycle, with constant flood for 2 hours following feeding. The issue as you point out is the amount of feed that you put in and the nitrates that come out. The other important point is that trout will eat significantly more feed in a given time than SP and this also needs to be taken into account. While the amount of food going into the system will determine the nitrates coming out, the number, type and growth rates of the plants in the beds will determine the ultimate concentration of nitrates in the tanks.

I have 5 grow beds with 28 trout that have been fed twice a day as much as they can eat, as is regularly recommended on the forum, and elsewhere. At the recommended stocking rate of 25 fish per 500 litres of filtration it appears one has 2 choices. 1) to have less fish but grow them at their maximum rate; or 2) more fish growing slowly; with the net result of the same amount of food being used and in theory the same mass of fish out the end. (I'm not sure that that point comes across very clearly on the forum when people ask about stocking rates)

The question also needs to be asked is there a benefit in having a smaller number of larger fish than a larger number of smaller fish? In other animal industries more usable meat mass is produced from a larger animal and is therefore more efficient, than a smaller animal as there are losses due to bones, guts, head etc. On the other side with larger fish you can run the risk of converting food to fat.


I did ask Faye and she does not know what her nitrates are but will test.
Interestingly Faye quotes in her thread that she gave her trout 5 cups of food in the morning and 5 in the afternoon.


Yes, good questions. How many people check their nitrates on a regular basis? Given the rates Faye is feeding it was not unreasonable for someone with the same size system to grow a third as many trout with significantly less food (there was no way I would have fed 5 cups in a day!) and expect that the nitrates would not be this high. Secondly the test kit only goes up to 160 and is not the easiest scale to read. Sure I was aware it got to (or past) 160ppm but as the forum does not flag massive nitrates as an issue (with trout) and with others applying similar high amounts of food in similar sized systems, the fiddling around to work out the higher rate was not a priority. Ammonia was and was tested every second day.

A good leaning curve and no losses.
All is well that ends well. Trout will take nitrates in the vicinity of 800ppm for several weeks it would seem.
And finally,
test. test and test.

Thanks Gavin.
I will bear that in mind for next season.
In the mean time I'm opening up a Jenny Craig centre for trout.

Out of interest I tested my parameters tonight Marc as I always have high nitrates too which I normally ignore, I havnt tested my system for a long time so it got me thinking. I have 30 SP, 5 trout and a handful of yabbies and marron. 1500L FT, 800L GB.

I feed lightly with one/two handful of pellet for trout per day and a handful of prawn for the SP. Yabbies and Marron eat the scraps/leftovers.

The results 5 minutes ago..

TEMP:12deg
PH: 7.2
AMM: 0
NITRI: 0
NITRA: 300-ish

Once again Im dazzled by my nitrate results, my beds are well seasoned and planted to the hilt. Im stocked nicely for this size system yet Ive never seen low or nil nitrate values. I have always fed lightly. It will be interesting to see what effect my DWC has because Im thinking I still need more GB/plant uptake.

I will be pulling some trout out soon and will post size but Im assuming only around the 300g mark.