Backyard Aquaponics
A place to discuss aquaponics

I have about 200 small SP in 5.5KL system. I've had them since fingerlings for about 3 months now and all has been well. I'm in the Adelaide Hills and its naturally very cold so they haven't been eating much for a long time now and gone quite dormant.

The water is around 9 degrees right now (2pm) I think (coffee thermometer (don't ask)), air temps can get down to 1 or 2 but I'm unsure what the water temp is at this point since my computer monitoring is on the fritz currently.

Last week I lost one fish after a particularly cold night this morning I found two more dead ones. One may of been dead for some days the other was mostly dead so I had to dispatch it The dead ones appear to be among the larger.

Last month we had lots of rain, so pH was always sitting around 7 and I stopped checking as frequently as I should, today I rechecked and it about 6.4 so I've now buffered it up again and will recheck tonight and push it back up close to 7.

I never use air stones and just spray the incoming water, I've done this with up to 50 mature active trout so I doubt it oxygen deficiency but I've now added an air pump just in case until I resolve this. All the fish just hang around the bottom I never see them coming up which I would expect if oxygen was low.

The dead fish do appear to have scale/skin sores around the face so here are a few of pics in case its a disease or parasite, I have no experience in this area.

Please help, I want to keep the remaining ones alive and healthy.

Being cold they would not be eating the same as mine were at that temperature.

Have you salted the water if not it would not hurt 3 ppt or 1 kg per 1000 litre of water.
I keep my PH around 6.5 or just below this time of year until the water heats up and they are feeding again. I then try and maintain between 6.5/7 ph but it always seems to be at the low end.

I've no idea what the problem is, but the lesions definitely don't look good. I'd do what ccBear suggested and salt to start with. I did come across this which has some photos and descriptions of diseases, it may or may not be of use to you.

http://www.dpi.nsw.gov.au/__data/assets ... Manual.pdf

Sorry I'm not being helpful, best of luck with whatever is wrong, I hope you can get it sorted and don't suffer too many more losses.

Thanks Guys

Any particular salt better than another, I'll pop over to Bunnings soon. I'm guessing they would sell pool salt with no nasty additives?

Yup, they sell a 25kg bag of pool salt for about $7 which is ideal.

I like the fine stuff you get from pool shops, pay a bit more but dissolves quicker. As long as it is pure salt and Bunnings is good for the price. Cheers

I grabbed a bag and stirred it in a bucket before adding to my sump. Seemed to 80% dissolve before I poured in.

How often and for how long do I need to do this?

The salt will always be there as the only way you remove it is when you do water changes or extra water from rain dilutes. Theres a instrument you can get from ebay which measures sat levels. Have one but forget the name.

Keeping a level of 3 ppt is good for the health of your fish and the plants are not effected at that level.

Similar to this listing http://www.ebay.com.au/itm/New-RHS-28AT ... 080&_uhb=1

With 5,500L of water, you're going to require a LOT of salt!

This winter I've been dealing with a few problems with barra (yes, I'm (foolishly experimenting?) over-wintering barra in an unheated outdoor system resulting in some sickness); here's what I have done and it seems to have worked pretty well so far:
1) Responsibly dump most of the system water, leaving "just enough" for the fish.
2) Isolate the growbeds, for the meantime.
3) Rapidly add enough (mostly pre-dissolved) salt to bring the salinity to 10-15ppt (for SP and barra) (note: 1kg salt per 1000L of water approximates 1ppt, so you need 10-15kg of salt per 1000L of water to achieve 10-15ppt salinity). Some undissolved salt on the bottom of the tank isn't a a problem and creates a localisation of higher salinity which some fish may exploit themselves. BTW: seawater is about 35ppt (35kg salt per 1000L of water).
4) Keep adding air and if possible keep the water slowly moving.
5) Maintain this high salinity for 6-12 hours (but be ready for start dilution using top-up water if the fish start showing signs of distress)
6) After the time has elapsed, bring your GBs online (you do need to flush some salt through the GBs for any water-borne nasties lurking there) and start adding sufficient top-up fresh water to dilute the salinity to 5-6ppt.
7) Repeat every few (3-4?) days until you see signs of improvement.
Keep your salinity at 3ppt for a few weeks thereafter, then let it "naturally" reduce to about 1ppt and maintain it at that level for good fish health.

SP can handle up to about 15ppt salinity for up to 15-18 hours, but your plants wont! Use the time to remove/replant any salt intolerant plants (such as strawberries, and for me cucumber (but some people don't have issues with them like I do?!))

Salt is not used up in a system per se, so whatever you add will remain there (within reason) so if you don't have a salinity meter then keep an accurate record of how much salt and water has been added and this should approximate (pretty closely) the actual salinity in the system. (Personally, by putting a drop of system water on my tongue I can taste salinity above 3ppt, although if you've got a disease in the system I don't recommend doing this too often!)

WARNING : Be careful as too many rapid changes (salinity, pH and temp) can cause extreme stress in the fish and kill them faster than the disease/parasite you're trying to fix. Consider bringing the FT water temp and pH close to the top-water levels over a couple of days first, and then slam in the salt as described above, but you do need to add salt rapidly so parasites don't have time to acclimatise to the new conditions (they adapt much faster than the fish!)

If you've only got a few infected fish then you can just remove them to a "hospital" tank with 15ppt salt for the required time and salt the rest of the system to 5-6ppt, but if you've got 200 small fish then it might still be easier just to do the entire system in one hit.


Hope this helps.

Thanks Bunson that was a great post. It looks like a lot of work if it gets the point of needing a full system treatment, but you got to do what you got to do. I'd be happier if I could definitively identify exactly what caused those lesions but I may never know. I have a 350L tank so I'm tempted to first see if I can hospitalise them. But I think I'll wait a little longer and monitor closely for now.

It isn't a flesh rotting disease is it? have experienced this with tropical freshwater fish which wiped a fair few out over a short period. Did all the dead fish have similar lesions on their head/bodies?

If you get in contact with a scientific laboratory in your locale, they should be able to point you in the direction of a lab/university/TAFE which can do the required analysis and can identify the source/cause of the ulcers/lesions.

I'm not sure, the earlier deaths occurred after very cold nights so I wasn't thinking disease at that point. I haven't netted any for closer inspection yet but I can see from the surface other fish that appear to have blemishes.

Judging from other threads 1KG of salt to 1KL = 1ppm? I've put in 5KG of salt so far, so I should probably put in another 10KG to bring it up around 3ppm, does that sound right?

From there I might try and use my 350L tank for intense salt baths up to 15ppm as suggested by Bunson then return them to the main tank.

I'm feeling very down about all this currently.

Hiya Bedlore, the salinity levels stated is in parts per thousand not million ie 1kg salt in 1000 litres is 1 ppt.

Thanks for pointing that out skeggley, just a "slight" difference.