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I will start by saying I am new to breeding corydoras and understanding water parameters. I am 17 and have been keeping fish for just over a year. I currently have a wild group of cw127 and wild group of pantanalensis. My tap water is ph7, kh8, hardness 140ppm, tds 240ppm. I have a salt based water softener as well as a ro/rodi unit. What would people suggest I do to soften my water to suit these species. I hope in the next couple of months get other species of corys such as cw160 and cw 146. Thanks for any info you can provide as I can not find a definite solution online.
Thanks,
Luke

Use the RO unit. Do not use the salt water deioniser as it will make your product water salty as it swaps other 'hard water ions' for sodium to make the water soft - what you want is low tds water which is what a good RO unit will do. In my experience you are unlikely to need to the DI unit after the RO for freshwater species but that will depend on the TDS after your membrane alone. Make sure again that that DI unit is one that does not get recharged with salt for the same reason as above.

edds wrote: 20 Apr 2025, 19:46 Use the RO unit. Do not use the salt water deioniser as it will make your product water salty as it swaps other 'hard water ions' for sodium to make the water soft - what you want is low tds water which is what a good RO unit will do. In my experience you are unlikely to need to the DI unit after the RO for freshwater species but that will depend on the TDS after your membrane alone. Make sure again that that DI unit is one that does not get recharged with salt for the same reason as above.

Thanks for the response, I have a tds of 5 after ro. Should I mix ro and tap water then?

Luckyloot wrote: 20 Apr 2025, 21:00 Thanks for the response, I have a tds of 5 after ro. Should I mix ro and tap water then?

Depends how soft you need it. I have kept blackwater fish in almost 0 TDS water in the past but you have to be meticulous with maintenance. I would mix in some tap water if it were me. You will need to research the breeding conditions needed for your particular species and go from there. Basically using 50:50 water will give you a TDS slap bang in the middle of the two values. More RO then softer. There is a way of calculating it using the two TDS values and the desired TDS value but I can't remember it, sorry!

Thanks, I will sell my water softner and buy another ro unit to make more water quicker.

Spend your money on a water butt and auto-shut off kit and then your current unit can fill the barrel with product water while you sleep, ready for you to use.

Some years ago I installed a 55 gallon rain barrel just outside my fishroom. Have never used my RO unit since. A 50% water change with rain water (my tap water is very similar to yours) has worked very well for spawning several corys.
-Shane

Shane wrote: 21 Apr 2025, 10:50 Some years ago I installed a 55 gallon rain barrel just outside my fishroom. Have never used my RO unit since. A 50% water change with rain water (my tap water is very similar to yours) has worked very well for spawning several corys.
-Shane

Thanks for your response Shane. I am just worried about the roof being dirty but I will look at possible solutions to this. I don't want to have all the waste water from ro so this is a great solution.
Luke

A first flush diverter can help deal with the dirt from the roof.