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Hello. I'm Ronny and am new in planet catfish! I've been keeping fish for 7 years now, and I'm planning to breed my Corydoras Elegans. I found somewhere that they breed with cooler water changes. My temperature is 79 Fahrenheit (26 Celsius) and I don't know how cooler the water should be. 72 maybe? I'm afraid of killing them since in my country we don't get rare corys often (aeneus, paleatus, sometimes julii and sterbai (really expensive)). How should I add the cooler water? Drop by drop?

Thanks for reading. Sorry for my english, I need to practice a little bit more.

Hi Ronngaribaldy,

First, welcome to PlanetCatfish! Glad to have you join the site, and I look forward to learning about your fish.

As for adding cool water, I'm sure different people do it different ways, and some ways are better than others. Myself, I simply add the water during my weekly water change: If I remove 3-5 gallons of warm water from a 10 gallon aquarium, I add the same amount of cool water back. I've never bothered to measure the water temperature with a thermometer while I'm pouring the water out of the tap, so I don't know exactly how cold the water is, but I do try to get a general idea of how cold the new water is using my hand. And I do use a thermometer to monitor the temperature in the tank as the new cool and old warm water mix together in my aquarium, so that my aquarium water temperature only drops a few degrees after the cooler water is added.

The bigger question is how much you want the aquarium temperature to drop. I've never worked with elegans, so I don't know what's safe for them, but the common species I have (aeneus and trilineatus) seem to do fine with a 5 degree drop, or even slightly more. Keep in mind that the warmth of my house will make that big 5 degree drop change in a few hours; if I go to bed with a 5 degree drop, the next morning the aquarium temp will be back to normal if my aquarium heater was running over night, or it will have at least warmed up a few degrees if the house heater was running overnight.

Hopefully someone with experience with elegans can give you suggestions specific for that species. But in the absence of that info... if you have the luxury of time and a second aquarium... you might try developing your technique first with one of the more common species, like aeneus, and then when you feel like you know what you're doing, then try it with the elegans.

Cheers, Eric

P.S., your English was fine.

As for how to add cooler water - I would do it slowly, and if possible near the exit of any filter. Cold water added to flowing water mixes much more easily then if added elsewhere

Looking at two sources- the information here on PC and then that on the Corydoras Encyclopedia site I see the range for elegans listed as 22 -25 C and 23 -27 C respectively. Most fish can manage a degree or two above or below such ranges for short term periods as well.

So the trick to dropping temp will be based on a few factors;
1. Current tank temp.
2. Desired tank temp.
3. % of water changed.

If a tank is at 26 C and the goal is to lower it to 22 C. From there is is simple math. Lets assume a 50% water change. Harking back to high school math,
50% of 26C + 50% of X temp, = 22C. or
(.5)(26) + (.5)(X) = 22.
13 + .5X = 22
.5X = 22 -13
.5X = 9
X = 18
So you would add water at 18C to the tank. This math works the same whether you are changing 25% or 75%.

But there are some other factors you might want to consider since what you will be doing is to simulate the onset of the rainy season. First, is the fact that the water arriving at the onset of the rainy season should be of lower TDS (hardness basically) than the current water as well as cooler. Making the water softer/lower TDS can be accomplished by mixing in some distilled water if the tank is smaller or else having an RO unit to make your own for larger tanks.

Next, as eric pointed out, the water temp will tend to rise back towards its normal temp. Many people will disconnect the tank heater for a number hours when doing a lower temp. water change to delay how soon the tank temp. will move back up. This will all depend on the ambient (room) temp. where the tank is. Also, other factors will come into play. Filters, pumps and powerheads tend to heat water to some degree and tank lights can do so to an even greater extent.

Despite all of the above, the odds are decent if you work to stay in a given range, the exact degrees are usually not super critical. In the above, if you are off by .5 or 1C, the fish won't really know the difference. In the wild there are no temp. controls and there is variability in water temps. Also, when fish are out of their safe temperature range and suffering from this, the solution is immediately to get them into proper temp. water. When you add the cooler water the only other factor is that it mix with the existing water. This can be accomplished by the force of the new water coming in causing it to mix or by turning a filter etc. back on during the refill. You are trying to avoid that 18C water creating its own zone as opposed to changing the overall temp. in the tank- think circulation.

Lastly, my experience, limited as it has been, is that of all the factors involved with the onset of the rainy season, the two most important are the barometric pressure changes that accompany the spring rains and the TDS/hardness of the water. I generally have not needed cooler water as well to trigger most fish. I have only resorted to it when a given fish has been stubborn about spawning. But I am also a big believer that to go the distance in simulating rainy seasons, the first step is to run a reasonable dry season.

I have found some fish will spawn just because of a local storm or just because of a water change. Some because these things happen together, and then there are cases where one has to work at a full cycle of dry and rainy seasons taken to the limit to get results. Being basically lazy and hating to do more work than I must, I have always started at the simple and easiest level and then if it didn't work, I took things up a notch and tried again. The problem is that, in the end, no matter what we may do, the fish will spawn when they are ready. The other side of this coin is they will often spawn even though we have not done anything specific to encourage it.

None of the above has dealt with conditioning the fish by providing then with ample high protein foods. But, that is another discussion.

I tend to do it over a slow period of time, i would look at the temperature range, keep it at the highest range and very gradually take it to the lowest range, when triggering Corydorus Paleatus, I was a bit more liberal with the cool water changes. But then you're working with a rarer species, so if it were me, I would montitor them more closely when making changes and even possibly increase the ammount of cool water going in over a longer time and see what the breeding response is.

Don't make the change instantly. What I do is drain down lets say 50%. Then I had several gallons of cool water and wait 15-20 mins then add more. I keep doing this until it is full

I think the atmospheric pressure can be an important issue, as mentioned above.

My 1-year-old Farlowella vittata spawned 3 times in a month just before Christmas, as several storms came through. Then nothing until this week and another storm. The cool water change probably helps as well.

I think also adjustment to the water levels of the tank can be a trigger, ie by allowing some evaporation to occur and then topping it up.

If your intention is just to move the temp down, why not popping a few small bags of ice cubes over a period of time and let it melt. I am assuming you are not running a huge pond.

Adjusting the temp is one thing but how do you plan to maintain it ?

Wow! I didn't think I would get this much advices! Thanks!

I'm feeding them with bloodworm twice a week and sinking pellets for catfish everyday. Since I'm from the Caribbean I have hot weather almost all the year. Reaching the 26 C was hard, usually the water stays in the 30's.

I'll try almost all of your suggestions, I'll let the water evaporate for 1-2 weeks maybe, and then add cool water trying to achieve the 20's slowly. I've the corys in a 15 gallons planted tank, moving them tomorrow to a 5 gallons, with bare bottom and a sponge filter, covering the sides of the tank with Styrofoam to keep the temperature and with a PC cooling fan over the top. Maybe with this measures I'll have them breeding in one month. I have an humongous R/O system at home so having fresh R/O water will be easy. Should I add a little bit of tap water and then replace the water of the aquarium with R/O water only? I'll do everything you suggest me, and I'm not in a hurry.

There's just one problem. They're 4 males and 1 females (If I'm guessing right). I'm scared to lose this only female lowering the temp.

I've breed aeneus before, they were quite easy, just a week after trying, but this girls are a little bit harder.

Thanks for all your advices. I'll keep you updated, maybe I can show the fishes tomorrow.

Cheer, Ronny

If the natural weather keeps your aquarium too hot, and you can't keep your aquarium cool for any length of time, you can try this: I read once that you can take plastic water filled bottles and freeze them then float the entire bottle in the aquarium. This is simply a variation on the "bags of ice cubes" idea mentioned above, which allows you to refreeze the bottles after they thaw out.

Hi Eric.

I can keep my water at 26 C with some measures, placing the tank in a place that I don't like, but is cooler, high evaporation and high aeration. I reached 23 C yesterday with the lights off. I have 12 plastic bottles filled with R/O water in the fridge ready to be used. My concern now is: How long should I fight to keep the water cool? I found a website where the author said that he made cool water changes twice a week and they breed, but I don't know how many degrees down and if he left the temp. to raise after the water change.

Just placed the fishes in the 5g aquarium with water of the old aquarium, filter media and a small powehead, barebottom. Temp is now in 23 C. And also took some pictures.

Ronngaribaldy wrote:My concern now is: How long should I fight to keep the water cool?

I think the answer to this is highly variable. As someone else mentioned, for some of my fish I will simply add the cool water, drop the temperate 4-6 degrees (sometimes a little more), then not turn the heater back on. The temperature will rise naturally over several hours, but without the heater it won't get as high as it was originally (maybe 1-3 degrees cooler). I'll leave it like that for a few days and if no spawn occurs then I try again.

Cheers, Eric

Thanks Eric. I'll do that.

I'll place a heater and set the temp at 26 C, water changes twice a week with 18 C water (adding ice), turning off the heater right before the water change. I'm thinking about replacing the pump for a sponge filter. What do you think?

I'll keep you updated.

Regarding the sponge filter idea, my corys often spawn in strong water currents. If this is your only mechanism for water circulation, then maybe a sponge filter is not the best idea. However, not all species have the same preferences and some just don't seem to care at all, so it really can't hurt to try that.

Hopefully someone with personal experience breeding this species could offer better advice. @fishdoc313? @mvinyl? Do you folks have any insights you can offer? Thanks.

Cheers, Eric

If the fish are ready to breed, they'll often breed within a few hours of the water change that lowers the water temperature - usually lowered about 3-5 C. If they do not breed right away, let the temperature come back up and try again. That's the conservative approach I have used for hundreds of breedings.

I understand you don't want to lose your elegans (1 female to 4 males is fine). I would not gamble with a larger water change, but I will share that my first breeding of corydoras was 40 years ago and it was corydoras aeneus. I was using water straight from our outdoor spigot, which was probably 30 F cooler than my tank. One of my children fell and cut themselves badly and I left the hose running into the tank. By the time I got back, my temperature had dropped from 78 F to 55 F. I cried, thinking I'd killed all of my best corys. The next morning I found hundreds of eggs. I later learned that this was how to breed them, I did not know that. Although NO ONE recommends that large of a temperature change (and not one fish died). It is amazing how resilient they can be.

I think you were doing fine before your first post and I think the advice you have been given will make it even more likely to be successful.

Then there are the following facts to consider. The onset of the rainy season is preceded by a barometric pressure drop. So timing one's cool water change to coincide with the arrival of a storm- be it snow or rain, often helps. Next, that same rainy onset not only brings cooler water, but it is usually lower in conductivity/TDS and pH as well. One last thing, conditioning by upping protein in the diet helps as well. Live worms are the best if you want to go to the Nth degree.

As mentioned above, some people get spawns with minimal effort and others have to work on it. In the end, nothing we can do matters if the fish are not "willing to cooperate." When the fish are ready to spawn, little we do (except segregate the sexes) will usually prevent it.

Apropos of that I have the following story which is the opposite direction. I had a 40 gal. breeder tank which held a pair of discus, a small school of rummy nose tetra and a group of L450s. There was a heater malfunction and I fount the tank at about 104F+ (40C). The discus were dead, the tetras were mush balls but all the L450 were hunkered in caves and alive. I dropped the temp as fast as I could and removed the dead fish. A few weeks later the 450s began to spawn. It was almost as if they were fireproof.

Hey all, Ok regarding my breeding of C. Elegans. They are in a 24" x 12 x 12 with 30w t8 lighting. Temp is 26 degrees C with a filter on full flow in the guise of a 280 LPH Jewel powerhead with sponge attached. The tank has a half inch of sand on base with 2 large amazon swords planted in opposing corners. These cory's love to lay on vertical surfaces and always choose the swords where they touch the glass and always on the reverse of the leaf. Ok so 2 days before I know bad weather is coming using a weather app I do a 50% water change using cold water, this takes the tank to around 22 degrees. So by the day of rain the fish will be slightly agitated in the morning leading to the usual chasing and the females submitting by early afternoon. eggs are laid in clusters of up to 15 and are very small eggs, raising them is relatively easy with micro worm, bbs and rotifers. ok some facts about the water I have. Its PH 6.7 (no bogwood just alder cone) Nitrite 0 nitrate 0 gh 8 kh 6. Mine lay all year round and are prolific breeders every 2-3 weeks.
Good luck with your attempts. regards MV