I’ve recently bought 2 mollies and 2 guppies ( these are my first fish) and had set up the tank following all the instructions careful , I have the water set at 26 degrees Celsius and left the tank with the filter on for 48hrs .
Fast forward to having the fish in the tank for 48hrs and I woke up to find one of my guppies dead at the bottom of the tank ( I’ve removed him and have him set on the time in a small bowl with tank water ) and now my two Mollies are acting strange and staying to the bottom of the tank ( still moving their fins but not swimming properly )
Iam really worried that I have done Somthing wrong regarding the tank but have no idea what and really don’t wanna cause anymore fish to die ! and everything online says it’s either too hot or cold in the tank but the thermostat says it’s the perfect temperature?
Unfortunately, you've been given poor advice and your tank is not cycled. It takes 4-6 weeks to cycle a tank and you must add a source of ammonia to do so. Just setting it to sit for 48 hours does nothing. This means that now you've added fish they are producing ammonia and as the tank is not cycled it is not being converted to safer forms and so is poisoning the fish. You need to get a liquid-based test kit urgently so you can track the levels of ammonia and nitrite in the water and follow the advice in the article linked below to deal with the problem. This is going to mean changing 50% or more of the water every day for a few weeks and you should start doing that immediately, don't wait for the test kit to arrive.
Did you use a liquid test for ammonia? Have you also tested for nitrite?
Regarding pH; it is very unlikely that the pH of your water would be too high for mollies and would not cause sudden death/illness in any case. What is the pH of your water? pH lowering products are not good as they often drop pH temporarily and then it bounces back, and will obviously rise again on water change. A stable pH is more important than the actual level, especially for hard water fish like mollies and guppies. The only truly reliable way to reduce pH is by lowering the mineral content of the water and that can only be done by mixing it with RO water or rainwater, but in your case, it should not be necessary.
Hi , the ph has been sorted and the fish are all doing a lot better ! I test by using the 6 in 1 strip test which are telling me the water is at the correct levels. So hopefully all will be well from now on .