My Platy fish is not active and betta's fin is not as colorful as before..

[wfykitty]

I just tested my water. From my understanding, we need to make PH lower and the rest are good. Is it correct? How to decrease PH by 1 and also how to decrease ammonia, nitrite, and nitrate in general?

 

[wfykitty]

Betta now is in a bigger tank

 

[eatyourpeas]

Your tank needs to be cycled. Here is the information:

Cycling Your New Fresh Water Tank: Read This First!

Cycling Your First Fresh Water Tank What is Cycling and Why is it Important? Fish waste, and especially fish breathing, plus uneaten food and other organic matter breaking down in a tank all produce Ammonia. This can quickly become toxic to fish if it is allowed to build up to any measurable...

www.fishforums.net

In the meantime, do 75% water changes daily so that the fish do not die. @Colin_T or @Deanasue can give you the play by play to keep your fish safe while transitioning.

 

[Essjay]

How to decrease PH by 1 and also how to decrease ammonia, nitrite, and nitrate in general?

Ammonia and nitrite should be kept at zero by water changes every time they read above zero. or by having a lot of live plants in the tank.
Nitrate should be kept below 20 ppm by weekly water changes - though this is difficult when it's higher than that in tap water.
pH should not be altered. It is in a complex relationship with GH and KH and you cannot safely change the pH without altering all three. Hardness is the most important parameter of these three, and can be reduced by mixing tap water with reverse osmosis water, or some other form of pure water.


Platies come from hard water with high pH so it's not a problem for them.
Bettas are soft water fish and should really be kept in soft water though the typical betta that we buy has been commercially raised for so long that it can tolerate harder water and higher pH than wild Betta splendens. GH up to 15 dH and pH up to 8.0 is OK.