Backyard Aquaponics
A place to discuss aquaponics

My Dad has just emailed me to say his system has lost a couple of his prize perch.

Better give you some back story.

This system has been nothing but trouble. When we first set up the system, we killed 100 silver perch within a fortnight as we had a freak cold spell (and the bacteria weren't colonised). After that, nothing would survive (tried silver perch & catfish). Eventually got 10 goldfish to stay alive. Figured the problem was an accumulation of gunk (uneaten food & waste) on the bottom of the tank. Rearranged the pump so it does a better job of clearing out the gunk, all good. Clear water. Got a couple of silver perch to survive.

Added 100 Australian Bass after the others had been alive for a month or two. All good. Suspect some predation because the SP's are a lot bigger than the bass.

In the last couple of weeks, he's been pulling occasional Bass floaters out but overall they've been doing well and growing.

On New Years Eve, the temperature got to over 45 degrees in the shed (where the fishtank is) and it was 44 in the shade by the house, and then it didn't get much below 30 degrees overnight after that, so the tank water (about 1400 litres) would have warmed up. I dipped my hand in on the afternoon when it was 45 degrees. It wasn't cold, but it certainly wasn't lukewarm either. Of course it then had the rest of the afternoon to continue heating up and I didn't check the temp after that...

As far as I know he's only lost 2 SP's (out of 3 or 4 that were alive) and still has a healthy population of goldfish and a reasonably good school of Bass.

Has anyone else had problems with overheating their fish?

Heat is a big issue. SP are meant to survive from 2 degrees up to 37.
mdbc.gov.au factsheet
Also dissolved oxigen becomes scarce I believe, as the temperature increases. Does your dad have any airstones?

Jimmy KP is right on target about the DO problem. Your dad's fish are very likely dying from lack of oxygen. I've been experimenting with some different types of heating/cooling and the one thing that looks promising for cooling is coils of flexi pipe buried underground. I don't have a big system to test but with my 350L tank, I was able to get 5C cooling in 4 hours with 15M of 1/2" pipe buried 1.5M under. Of course, it's our winter and I don't have the outside temp to contend with so the test was limited. My ground temp 1.5M down was 19C. I actually heated the water first with solar and then turned on the flow to the coils. It seems the good earth can dissapate a lot of heat. Not sure how long it would do that but it might be something to think about. Good luck.

The earth can yes, I've seen a couple of systems (not AP) that use the earth for water cooling lines. However I think your experiment was a little uncontrolled. I'd like to know whether you could keep the tank cool, if you left the solar heater on. Try it with an external heat source I mean. See if you can keep the tank at or close to ambient.

Whoah! That is a much larger range that I've read elsewhere. Are you sure? (I couldn't find anything about temperature range on that fact sheet.)

Perhaps I've only read _feeding_ temperature range in the past?

My bad. I have the actual pdf fact sheet. I just copied a link from within it. download the pdf and it has temps

from mdbc.gov.au hope they don't mind...

LARVAE AND JUVENILES
Movement : Larvae swept downstream but juveniles move upstream &
downstream during increased flows (88, 186, 188, 189)
Habitat : Benthic habitats in backwaters & floodplain areas rich in
zooplankton (88)
Temperature range : 2-37°C (153)
Salinity tolerance (mg/L) : <24,600 mg/L (125)
DO tolerance (mg/L) : Data deficient
Other :
ADULTS
Habitat : Turbid, still & slow flowing waters in main channel & large
anabranches, & in large floodplain lakes during major
floods; prefers open water with nearby cover from littoral
macrophytes and woody debris (45, 49, 155, 156, 174)
Temperature range : 2-38°C (49)
Salinity tolerance (mg/L) : <15,000 mg/L (105)
DO tolerance (mg/L) : >2 mg/L (287)
Other :

Well, I am 99% sure the temperature didn't get to 37 degrees in the water - my guess is it was in the mid-20s when I tested in. Of course, the growbed would have been acting like a big ol' solar heater that afternoon... Although, some back-of-the-envelope calcs tell me that with a 1500L tank, an absolute maximum (assuming 100% absorption of radiation) of 7 degrees C could be attributed to the growbed acting like a solar heater, and more like a couple of degrees.

He has a large airstone operating 24/7. I'll check with him to make sure it's still working.

As far as I know, the only unusual deaths (in this AP system a certain attrition rate has become "usual") were these large silver perch. By 'large' I mean 15-20cm long. The Bass are 3-5cm long. This indicates it could be a size-dependent issue, or a species-dependent issue. Or both.

What are you water specs.... can you test and post?

The larger fish are more likely to die of DO related problems and/or will die quicker when DO is too low.

The fact that you have a "usual" attrition rate is a concern and would indicate there are some weak points in the system or its management.

Except for mortalities in the first few days after receiving fish - I've never had any fish die.

you have to be careful with guessing water temp by feel. It's very relative.

A couple of days ago on a 40+°C day, I dunked my hand in the water, and thought it felt a lot cooler than the 30°C that the thermometer said.

The next morning, after a cool night, I felt the water and was surprised that it was a lot warmer...then looked at the thermometer - 24°C.

The difference was the low air temp, which made the water feel warm. So on a 45° day, expect the water to feel a lot cooler than it is.

A demonstration for you, borrowed from New Scientist:
Dunk each of your hands simultaneously in separate bowls of water, one hot one cold. Then put them both in a third bowl, at room temp. The hot hand will tell you the water's cold, and vice versa. Would freak the kids out I'm sure!

Moral: Get a thermometer. It also pays to observe fish hunger vs temp, because there is a strong correlation. If the water's warm and the fish aren't very hungry, something could very well be up with them.

Cheers

We had a thermometer, but it was one of those "indoor/outdoor" ones - we just wrapped the outdoor temperature probe in a plastic bag and dangled it in the water. Worked for a while, but then stopped.

It looks like DO is the cuplrit:
http://www.newton.dep.anl.gov/askasci/c ... m03334.htm

Warm weather = lower oxygen retention in water + higher metabolism of organisms (i.e. higher demand for oxygen and less oxygen available).

Looks like we need to get an air pump with more balls...

I'd add a thermometer, and a pH, ammonia, nitrite and nitrate test kit to the shopping list as well Jimmy

So far you've had threads relating to uncycled systems (pH and ammonia), cold water and now hot water...... all of which in one way or another have resulted in an almost perfect 100% record of fish kills...

Do yourselves a flavour.......... grab a test kit, understand the nitrogen cycle, relationship of pH and ammonia, pH and nitrites, temperature and oxygen....

And test and monitor.....

Either that or just buy tins of sardines... it'll be cheaper

Hey Rupert, that's unkind.

This is my Dad's system, I live an hour away, and I just got the email this morning that his Silver Perch died. I'm just trying to help him out. He hasn't been answering his phone so I'm flying blind.

We have the test kits you mention, but need to use them more religiously.

As far as understanding the nitrogen cycle, and the relationship of pH, temperature and ammonia tolerance, well, we found out about those things the hard way when we tried to establish a system in the cold weather. Have only just learnt about DO and temperature relationship today - I guess with the splashing from the return line and the large airstone bubbling away in the tank itself, we've never considered the need for further aeration. Now it seems as though this explains the latest silver perch deaths.

So we're learning (albeit the expensive way)! Thanks for all the advice.

Cheers,
James.

Jimmy - the first part of the 2 part 'Healthy Fish are Happy Fish' article in the 1st edition of the Backyard Aquaponics Magazine' would be well worth a read for yourself and your father.

By the way, what sort of wattage do you guys have on your aerators, and for what volume of water & mass of fish? That way I can select an appropriate one.