When was the last time the water was changed in the fish bowl?
How often and how much is the fish fed?
Hi again John and thank you for the detailed explanation.
Simply stated the problems you are encountering are due to unfavorable water conditions caused by the rapid formation of ammonia which as you know is lethal to fish.
What needs to be done in order to maintain the fish healthy, thriving and alive is change all of the water in the bowl every other day making sure to use dechlorinated water that is the same temperature as the water being discarded. By doing this you'll be assured that harmful ammonia and nitrites cannot form thus saving the fish from any potential health issues.
It's also important to not overfeed the fish as excess feeding leads to excess fish waste which is a major cause of ammonia formation. Feed the fish only a small pinch of food once a day. Note that a fish's stomach is approximately the size of its eye so not much food is needed to meet a fish's dietary needs.
The cloudy/misty water you saw was an indication of beneficial bacteria forming as a result of the presence of ammonia in the water.
Also be aware that 2.5L is not a lot of water and only 1 guppy should be housed in it as if more fish are added more waste will be produced at a quicker rate thus the quicker that lethal ammonia will form.
I'd suggest ceasing the use of Melafix as there is not a disease issue here but more of a water quality issue. Instead of adding Melafix add a pinch of aquarium salt with each water change. Incidentally a ph of 7.5-7.6 is not dangerous for guppies as it is for some other fish so there's no need to worry about a ph issue.
The most important thing here is to maintain good water conditions and your fish will thrive.
You stated-"But the people who sold me everything, don't seem to give a damn, and i even told them, that i am a complete beginner with fish and don't really know anything about them, and then he just lets me buy 4 guppies." You are absolutely correct and I agree 100% as the goal of many pet stores/shops is to make money and not to have a customer with healthy fish as the more problems a customer has the more likely they are to return to the pet store for products.
Best wishes and please let me know if you have any questions.
Hi John. I'll address all of your questions in the order you posted them.
1) It's no problem if aquarium salt is added to water that contains Science Products Complete Water Treatment and Melafix but keep in mind what I mentioned earlier in that it is not necessary to add Melafix as the fish is not suffering from a disease. Also as mentioned prior all of the water should be changed every other day whilst adding the corresponding amount of Complete Water Treatment and aquarium salt. Changing the water every 2 weeks will cause a water quality problem.
2) Aquarium salt should be added with every water change but only the amount that corresponds to the amount of water being exchanged/changed. As for the frequency and amount of water changes, they can be done every 2 weeks if fish are being housed in a larger body of water but in a small amount of water such as that in your fish bowl it's best to change more frequently.
3) Yes what you stated is true about the qualities of the Science Products Complete Water Treatment but it's ammonia binding/eliminating effect is only temporary thus the high ammonia level you witnessed in the water. When a product states that it "locks up ammonia" it is basically saying that it neutralizes it. You can continue to use the Water Treatment when doing partial water changes as it will eliminate/neutralize harmful additives that may be present in the water source you're using.
4) I do not recommend that any more fish and/or snails be added to your bowl as further additions to the bowl will place undue stress on the biological balance of the water in the bowl.
5) (Addressed in #4)
6) The light on the bowl should only be on when viewing the fish and performing maintainance on the bowl as excessive light will cause unsightly algae to grow.
Guppies sleep/rest whenever they desire and sleep deprivation is not an issue with them. They have no set rest/sleep time. What makes guppies ill is stress usually caused by unfavorable water conditions which leave them open to a variety of diseases.