If the guppy had a big white patch (5-10mm) on its back it did not have white spot (Ich). It probably had a bacterial infection, however without seeing it I can't be 100%.
Fish have a thin layer of mucous over their body and fins. If fish are stressed by something in the water (ammonia, nitrite, medications, chlorine, etc) they produce more mucous and it can look like they have a cream or white film over their body and fins. If fish ever get a cream or white film over their body and fins, do a huge water change and gravel clean the substrate, and increase aeration/ surface turbulence.
Fin Rot is caused by poor water quality and can normally be cured by doing big water changes, gravel cleaning and increasing aeration. If the fins get red lines in them and continue to deteriorate after several big water changes, then you might need a medication, but water changes should be the first course of action.
Small white dots (about the size of a grain of salt) on the fish's body and fins is white spot (Ichthyopthirius) and should be treated.
White patches or spots on crayfish can be fungus or something else but pictures are required to ID issues.
Soft water (low mineral content) can have a lower pH that can cause fish to get a milky white edge to the tail and damaged or split fins (Fin Rot). This is more common on fish that naturally occur in hard water and rarely seen on fish that come from soft acid water.
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Never treat fish unless you know what the problem is.
Prophylactic treatment of fish or any animal is not recommended due to the chance of disease organisms developing a resistance to the medication.
The only thing you can do as a preventative treatment for fish is deworm them. All fish should be dewormed in a quarantine tank before being added to the main display tank. If you don't have a quarantine tank then just deworm all the aquariums in the house at the same time.
Most fish health issues are caused by poor water quality and doing a 75% water change and gravel cleaning the substrate each day for a week, will usually fix most problems. At the very least the big daily water changes will dilute disease organisms and buy you time to work out what is going on and start treatment if needed.
The following link has information on what to do if your fish get sick. It's long and boring but worth knowing. It is basically a more in depth explanation of what I have mentioned here.
http://www.fishforums.net/threads/what-to-do-if-your-fish-gets-sick.450268/
Fish have a thin layer of mucous over their body and fins. If fish are stressed by something in the water (ammonia, nitrite, medications, chlorine, etc) they produce more mucous and it can look like they have a cream or white film over their body and fins. If fish ever get a cream or white film over their body and fins, do a huge water change and gravel clean the substrate, and increase aeration/ surface turbulence.
Fin Rot is caused by poor water quality and can normally be cured by doing big water changes, gravel cleaning and increasing aeration. If the fins get red lines in them and continue to deteriorate after several big water changes, then you might need a medication, but water changes should be the first course of action.
Small white dots (about the size of a grain of salt) on the fish's body and fins is white spot (Ichthyopthirius) and should be treated.
White patches or spots on crayfish can be fungus or something else but pictures are required to ID issues.
Soft water (low mineral content) can have a lower pH that can cause fish to get a milky white edge to the tail and damaged or split fins (Fin Rot). This is more common on fish that naturally occur in hard water and rarely seen on fish that come from soft acid water.
------------------------
Never treat fish unless you know what the problem is.
Prophylactic treatment of fish or any animal is not recommended due to the chance of disease organisms developing a resistance to the medication.
The only thing you can do as a preventative treatment for fish is deworm them. All fish should be dewormed in a quarantine tank before being added to the main display tank. If you don't have a quarantine tank then just deworm all the aquariums in the house at the same time.
Most fish health issues are caused by poor water quality and doing a 75% water change and gravel cleaning the substrate each day for a week, will usually fix most problems. At the very least the big daily water changes will dilute disease organisms and buy you time to work out what is going on and start treatment if needed.
The following link has information on what to do if your fish get sick. It's long and boring but worth knowing. It is basically a more in depth explanation of what I have mentioned here.
http://www.fishforums.net/threads/what-to-do-if-your-fish-gets-sick.450268/