Do you mean when I added them to the tank? Let them float, added water, let them float some more, added a little water, etc then added them? I did do that
Okay, so it sounds like you did acclimate them to your water. I hope you did not release the water they came in into your tank. This is not recommended to do as the water, no matter how good it was when it went into the bag, changes when in the bag with fish and ammonia becomes present and is needlessly added to the tank when you add the water into the tank.
Assuming that you didn't do that, it sounds to me like you got healthy fish but put them into water that was not suitable for them. Whether it was the lack of minerals or TDS or just the saline aspect, that is why they didn't last long. Again, this is assuming that these were the first fish into a new set up and that new water had been neutralized of chlorine or chloramines. New water does not kill fish because the filter bed is not cycled. So that's off the table.
If there is just the frog now and no other fish, you can do 1 of 2 things. 1- just empty the tank of the water and replace it with new water. This new water should have no ammonia, nitrite or nitrates. Your frog lives in the water but breaths air so it's not effected by the massive water change. ( Keep him in a separate container while changing the water to reduce his stress.) You can then try adding 1 or 2 fish to do a fish in cycle.
2- leave the tank as is and let the frog's food and poo be the ammonia source needed to cycle the aquarium. What you are trying to achieve is a balance between ammonia producers ( fish, frogs, aquatic life) and ammonia consumers ( nitrifying bacteria). You are creating an ecosystem that when properly set up, keeps the tank healthy. The 2 stage process ( Ammonia to Nitrites, Nitrites to Nitrates) takes a little while and can kill fish as the first stage creates a toxic environment under certain conditions. The end result, Nitrates, can be controlled also multiple ways. 1 is by water changes, another is by plants using that nitrogen source as fertilizer. ( Old fish water does my garden plants wonders
) There are also other filtering products supposedly that remove nitrates.
So if you are doing your tests, you should see a rise then fall of ammonia and a rise and fall of nitrites ending in a rise in nitrates. If you were to plot this on graph paper, these 2 cycles would like like a Bactrian Camel ( 2 humps) with a rising neck.
Okay, so I told you all that so I could tell you this about water changes:
The amount of fish in your tank and subsequent nitrate level will determine how much water you should be changing and how often. In a properly stocked tank, the rise of nitrates should be slow. However, in today's " let's shove as many fish as possible into as small a tank as possible" mindset, Nitrate levels can rise sharply and quickly. In my tanks, I do a 10%-15% weekly water change to achieve a low nitrate balance. This is because I over size my tank and under size my fish load. I'm not saying I have large tanks. In fact, most of my tanks are 10 gal tanks with breeding pairs of Angelfish. But I just have the 2 fish in a 10 gal tank so the ammonia level doesn't go up high and the nitrate level never gets the chance to get high. So keep that in mind when you are stocking your tank. How will you know when you have "overloaded " your tank? Your nitrate levels will rise quicker than "normal" or what they used to do. So, for example, if your nitrate level rose 1 point in 7 days on average then you added more fish and it now rises 1 point in 3 or 4 days, you have (in my opinion based on the science I was brought up with) overloaded the tank. Keep in mind that this rate hike needs to occur after the initial adding of the fish. Ammonia levels will rise some whenever you add fish until the nitrifying bacteria bed grows to handle the load. This is why it is always recommended that you add fish slowly to a tank and not all at one time. I know there are products that claim that they eliminate this cycling process but that is probably a sale's pitch. The way I described is a much safer route to take. So if your nitrate level remains low for 7 days, you can just do that small change on a weekly basis. But do it every week! If the nitrate level rises higher than recommended in that 7 days period, you will be doing water changes more frequently than once a week. Certain fish do not handle massive changes in water chemistry so more frequent small water changes will serve you better than larger less frequent changes. Not overloading a tank is the best way to avoid that scenario all together.
I hope I have answered you question. If you have more ??? feel free to PM me
