My 5 gal has two female betta and a baby koi. For the past two months, the tank upkeep has been hell. I use the API test kit, and for some reason, the ammonia skyrockets almost everyday! I do 25-50% water changes nearly every day, and add ammonia detoxifier sometimes. But it seems the detoxifier causes the pH to plummet and I am worried about stressing my Ladies.
It's probably the fact you have 3 fish in a 5g, one of which is a Koi. What water conditioner are you using? You should be using one every water change, Prime is usually the suggested one. You do know that the Koi isn't supposed to be in a tank but a pond? Keeping it in a 5g is causing it harm. Tank size is determined by the adult size of a fish not its current size. I would rehome the Koi or build a huge pond.
Sorry, goldfish. I derped cause my parents have koi. But this problem has been going on since before I added the goldfish. I use Kordon products, like AmQuel Plus Amm detox and NovaAqua Water conditioner.
Goldfish are HUGE waste producers hence why you've had the problem since adding him. Goldie keepers will say one goldfish requires a minimum of a 20g. Also, they are not tropical fish like your Bettas. I'd rehome the Goldie.
Goldfish in a 5 gallon is what is giving you constant ammonia readings. The amount of ammonia a goldfish can produce is insane. This is one of the reasons they really require a large aquarium or pond.
Your tank is overstocked and poorly stocked. Two females are going to fight unless you have them separated (probably too stressed right now by poor water quality to do so) and a goldfish has no business in anything under 20-30 gallons.
I would remove the goldfish, separate the females either into individual tanks or use a divider in the 5 gallon and do at the very least a 100% water change to get your ammonia back down to 0. Anything over 0 is bad news, and when it starts getting up around the .5-1ppm mark you are going to start seeing the effects.
By removing the goldfish it is going to be so much easier to maintain proper parameters.
Rarely are female bettas that aggressive. Ive had sorority tanks before, and the girls I have in there now swim together. Whenever I add a new girl, I watch to make sure she isnt a...well..a meanie. But as to the goldfish, I had no idea.
Why do goldfish make that much waste?
And this still doesnt explain why I was having these problems BEFORE I added him.
I've also had sorority tanks before and females are as unpredictable as the males. Just because it has worked in the past doesn't necessarily mean it is going to continue to work in the future.
Goldfish have basically no stomach so what goes in just usually comes straight out. Their oxygen requirements are also much higher than that of a betta so you need a well-filtered tank. They also become severely stunted in small aquariums.
You mention ammonia in your source water? I am assuming your tank isn't cycled, so what product are you using to neutralise the ammonia in the first place before it goes into your tank?