Welcome to FishLore! It's great to have you with us! If you don't already understand the
nitrogen cycle, it is necessary that you do. We have some articles here on FishLore that will help out a lot:
http://www.fishlore.com/Forum/index.php?topic=620.0
The tetras and the swordtail will probably do okay, but your cory and otos will have a hard time being in a tank that is not cycled. Do not be surprised if you lose them. I would not normally suggest this to a newbie, but since you have delicate fish in that tank, if you can find bio spira from a reputable dealer in your area, you might want to invest in a 1 oz. pouch. Bio spira is the bacteria found in a cycled tank, so it is essentially an instant cycle. If you do decide on the bio spira, drain your 30 gallon tank completely if you already have your fish in it (temporarily moving the fish of course!), and then refill it. Add your fish back to the tank, and add the bio spira. You are probably already doing this, but just wanting to make sure, you are treating your water to some kind of conditioner like aquaplus, start right, etc., right? If not, you always need to treat your water with one of these products to remove
chlorine and/or chloramines from your water. A lot of them also remove heavy metals. If you have well water, you may not need to use these products unless you have metals in the water. If you go the bio spira route, your tank should be cycled within 24 hours. Using bio spira also works better when added with a full bio load of fish, so you could add the other fish you wanted to add right away. Keep in mind that this is another no no that is usually not recommended, but your situation is not the norm, and there will be the risk of having sick fish in your tank that could infect your other fish doing this. Save that 10 gallon for a quarantine/hospital tank. Normally when you get new fish to add to a tank that already has fish in it, you should put them in this quarantine tank to make sure that they are not diseased and exposing them to your healthy fish. You should always quarantine all new fish this way no matter where they came from. 1 sick fish can wipe out a whole tank.
If you chose to not use the bio spira and cycle the tank with your existing fish, you will need to make sure you have a good testing kit for ammonia, nitrite, and nitrates. My suggestion is the Aquarium Pharmaceuticals Master
test kit which goes for around $15.00 online plus shipping, or you can copy the page with the kit on it on the PetSmart website and take it into the store where they should honor the online price. Locally, you will normally pay around $30.00 for the same kit. Check your ammonia and nitrites daily. If your ammonia or nitrites go over 1.0, you need to probably do at least a 10 gallon water change to get them down. Your cycle will take longer when you do water changes, but you will have to do them if you want your corys and otos to have a chance of survival. First, your ammonia will spike then go back down. Then the nitrites will spike and go back to zero. Once your ammonia and nitrites are at zero, and you are showing nitrates, your tank is cycled. You don't need to add any more fish to the tank until it's cycled. Then you could add 2 fish at a time, wait for the ammonia and nitrites to go back to zero, and then add a couple more. Please make sure you research compatibility of the fish you want in the tank with the fish you already have. Adding more cory cats to the tank after it's cycled is a good choice. You will love their activity level when you get at least 5 or 6 in the tank. Also, keep in mind how many inches of fish you have now, and how many more inches you can add to the tank while deciding what to add. The general rule is 1 inch of adult fish per gallon, which really only works for smaller fish. So each cory is about 2 inches of fish. I would add the algae eater for last. You already have otos in the tank, and if there is no algae for them to eat, make sure you put fresh zucchini or veggie wafers in the tank so they don't starve to death. The swordtail will probably love the zucchini as well. Click on this link to check out the different suckermouth catfish that are available, and I would recommend you look at the ancistrus species which don't usually get bigger than 6 inches long. One would be a good choice for your 30 gallon tank.
www.planetcatfish.com
I know it sounds like a lot to learn, but you will get the hang of it quickly. A lot of our members are in their early teens and are excellent fishkeepers, and your son will be too once you get the tank cycled. At that time, you will get a condition called
MTS(multiple tank syndrome) which we don't try and cure here. It always starts out with 1 tank, but it's like the lays potato chip, you can't have just one! We encourage MTS here so don't fight it. You will be so proud of yourself when your tank is beautiful and cycled, and you will want another. I see that already happening.
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