Backyard Aquaponics
A place to discuss aquaponics

Good afternoon,

I have 2 x 500L beds (2 more to go in soon), 4500L fish tank sunk down 1000mm, 20 rainbow and 20 brown. System went in early Nov last year, fish went in end of November about 40mm.

Water has been very stable since Jan

Ph 7.6 (hasn’t budged since day 1)
Ammonia < 0.25
Nitrite 0
Nitrate <5

I was going to get a DO tester, but due to the Australia tax figured an air pump made more sense...

Temp around 16°C, though has been 18°C until recently (got up to a max of 24° during the heat wave, but was back at 20°) within a few days.

Water is amber colour, no solids to speak of in tank.

Pump is 11,000 Lpm with a fair bit of backwash to keep the tank stirred and fish active - duty cycle is 20 on 40 off (bed fills in 3 or 4 minutes, but still have cheap mech timer so that’s the smallest I can do).

Running air at 35 Lpm around the clock - though thermal cutoff means it has about 60-70% duty cycle.

Fish are perky, feeding well and frisky - blood was bright red and gills looked healthy and pink - mostly around 70g though there are some non eaters at 15g.

Did have 3ppt salt - but plants weren’t thrilled, now down around 1ppt.

Whenever I top water up, I spray it into a separate container and add sodium ascorbate to nuke any chlorine, but haven’t topped up in weeks.

I lost one yesterday and four today - the only thing out of the ordinary was I removed some greedy celery a couple of days ago - and it did stir up a bit of silt, night temps have dropped a bit and we moved to floating pellets a couple of weeks ago.

I ate one and it tasted great, no blotches or fin damage - clear eyes - flesh totally white but firm

This is my first system - but I actually thought I was doing OK having got through a once in a century heat wave this summer (during which, inexplicably, there were no deaths) and was considering getting a few more fish given the low nitrate levels, good water (apart from a small amount of ammonia) and temps coming down - but this has shaken my beginner’s luck confidence...

Can stirring up silt in the beds be an issue?

Could this be delayed stress from cycling/summer?

Any ideas?

Thanks.

Most of what you have explained sounds ok and doesnt explain the deaths. It is strange that you are seeing trace ammonia levels, what feed rate rates are you using and make sure there arent any floaters jammed in pipes or pumps etc as this could be pushing up the amm and stressing the others. Other than that certain levels of Sodium Ascorbate will see damage to the kidneys, upper respiratory tract and gastrointestinal tract. The dissacossiation of the Sodium ion and buildup in the system could also be a concern in the long term. Just add the tap water straight to the system no more than 20-30% of the total water volume.

Sodium ascorbate was added at 1/2 teaspoon perl 200L - but I’ll take your advice and leave it out in future (probably get a float valve).

Feed I’m a bit slapdash on, I just flick a few out about twice a day - if they don’t get smashed right away, I skip that feed - otherwise I put about 1% mass per feed. I now scoop up what’s left half an hour later (yay floating pellets!), but I’ll have a look and see if there are any leftovers hiding as you say.

I’m going to have to look up dissacossiation of sodium ion (wishing I hadn’t ditched chem all those years ago now...) - would you be changing water out to dilute? (Over time there’s perhaps 4 teaspoons gone in to 4500L).

Thanks Charlie.

Hmmm, thats certainly not an amount to be concerned about FD, no need for water changes. Also your feed rates are reletively small so cant see a problem there either.

As you say the fish looked healthy so not going to be an easy one to nut out.

Any severe rains or temp swings leading up to the deaths? Just spit-balling

Just a few mm rain last night - overnight temps have dropped a bit in the last week, now water starts out at 16° in the morning and ends up around 18° late arvo if we get a bit of sun.

Just cleaned out the air filtre (no build ups to speak of) - off to strip the pump next... (Edit: clean as a whistle)

I’m hoping that will turn something up, as we have never got rid of that last 0.1 ish ppm ammonia.

Is it possible your water source has chloramines? That may explain the trace amm

Ahhhhhh - good point. I just tested some from the tap and while it’s 0 ish, it does have a slight green tinge - if I’m calling my FT 0.1, I’d say 0.05 ppm - interesting because the water supplier claims not to use it in my area...

Chloramine is a combined chlorine/ammonia bond.. the chlorine will off-gass if exposed to UV in time... but it takes longer than straight chlorine.

Chloramine can actually feed the system due to its amm component, but this is why it is toxic to fish in large quantities and can actually crash a relatively new system or produce false and misleading readings. Top ups will be ok but if you need to do big water changes for any reason, you can actually compound the issue.

Neutralizers and activated charcoal filters can break the bond to free up the chlorine to aid in faster off-gassing but the amm component needs to be taken into account. Usually when using these options you need to take care as amm reading can return false.

I think it is best to have a barrel or 2 of "off-gassed" water on hand in case of large water changes are needed (+50%) if chloramine is a suspected to be strong a water source and as mentioned you are better off not using Sodium ascorbate anyways.

Will get on to that - thanks again for the advice.

Check with the local water board, I'm just providing info for you.