Corydoras and ph drop

[Irishlad123]

Hi im relatively new to the hobby. This morning when i woke up one of my 6 corys were floating i was schocked as she reciently laid eggs but could not do anything as i was late for a bus. I came home and ive tested the water and examined the body and the only oddity is my ph has dropped from 7.2 to 6.4. My tempeture is at 25 degrees celcius. My nitrite at 0 ammonia is at 0.25ppm and nitrate 10ppm. It is due a water change tommorrow. I change the water every week and a half. One corydoras did graze its face lately and it kinda went might but has healed by itself could this have spread a disease. No fish in the tank was aggresive. I did leave her out of the water this morning on the glass edge that is on the tank and when I examined the body it did have a reddish colour. Is this just from being out of the water. What could have caused this ph drop and how can i fix it.

 

[Byron]

The pH drop is not likely the issue here. But we should look into it anyway, so what is the GH, KH and pH of your source (tap) water on its own? Remember when testing tap water for pH you must ensure the CO2 is out-gassed as this can affect the pH result (only for tap water, not when testing tank water). Sit a glass of tap water out for 24 hours then test, or agitate a small amount of tap water very briskly and test.

When we know the GH and pH of the tap water we will have a better idea of the chemistry. What is the normal pH of the tank? This should be tested prior to a water change to get an idea of what it normally is, at least for a few weeks, then periodically.

 

[Irishlad123]

7.2 and i have soft hardness Current mg/l of CaC03 in your water18, SoftAverage mg/l of CaC03 for your Water Supply Zone23, Soft

 

[Irishlad123]

ibhave no kh gh test

 

[Byron]

7.2 and i have soft hardness Current mg/l of CaC03 in your water18, SoftAverage mg/l of CaC03 for your Water Supply Zone23, Soft

OK, this is easy to explain. The GH and KH are both low (ideal for soft water fish species, no issues here). The pH is likely to lower in an aquarium. This is normal, and due to the breakdown of organics, organics being the fish excrement, dead plant/fish matter if any, uneaten food. The breakdown of the organics is primarily in the substrate, achieved by various bacteria species, and CO2 and ammonia are released. [The ammonia is not usually an issue, we can leave that.] The CO2 increasing from primarily the organics, but also from respiration of fish, plants and bacteria, produces carbonic acid which lowers the pH. This will conitnue until the pH becomes stable in relation to other factors such as the GH and KH, and any influencing factors such as fish load, fish feeding, plants, calcareous substances, etc. It is always safer to let this sort itself out, and after a couple months the tank will be relatively established biologically and will tend to run from then on with little if any changes, provided water changes are regular, fish are not overstocked or overfed, etc.

That explains the pH, feel free to ask questions. I've no idea what caused the death of the lone cory, but again it is unlikely to have been the lowering of the pH. If you have other cories, check their rate of respiration (rapid respiration is a sign of water issues, though when feeding or physically active this can be normal). Be regular in weekly partial water changes of 50-70% of the tank volume (at one time each week).

 

[Irishlad123]

Ive had the tank over a year and a half now though so should it not be already established

 

[Byron]

Ive had the tank over a year and a half now though so should it not be already established

Yes, unless you do some major changes (a new substrate for example would reset things). You need to do pH tests regularly over a period of time to get a complete picture.

Test the tank water pH just before the weekly water change, and do this for several weeks. Keep a written record. Always test at the approximate same time each day you test, example in the early morning prior to the water change; pH does shift during each 24-hour period so to get a more consistent and accurate idea you need to be testing at say 9-10 am each time you test, or 2-3 pm, whatever. Early in the day is best because pH will be lowest then, and highest at the end of the day.

Also, test the tap water each time you test the tank, just to see if the tap water pH is fluctuating; remember to out-gas the CO2 from tap water.

You could also test the tank water the day following the water change, sporadically perhaps, to get an idea of the change resulting from the water change.

 

[Irishlad123]

Ok i will their has been no major changes to the tank except i took out a couple of plants and transferred them to a new tank