1. Is the hang-on breeder box with air stone circulated water from the main tank enough filtration, or do you think a separate grow out tank with conditioned sponge is necessary? So far, I’ve not had any issues over-crowding the breeder box because of low survival rate.
I don't use breeding boxes/ traps for fish. If I breed fish, they get put into their own tank (usually a 2 foot long tank for most fish less than 3 inches long) with an air operated sponge filter, some sand or gravel on the bottom, lots of plants or spawning mops and a heater. The males & females are separated for around 5 days before being added to the breeding tank. After they finish breeding, the adults come out unless they look after the eggs and young, the water level is dropped to about 4-6 inches and the babies are reared up in that tank.
I drop the water level for the babies so when they hatch and start swimming around, there is less water and the fry are closer to the food. This means the babies use less energy to find food.
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2. I have not been doing water changes in the first 48 hours after hatching because I’m not yet feeding them and they are still absorbing their egg sac and not producing waste—in theory. Is this wrong?
2.1. If I’m hatching the eggs in RO water with hydrogen peroxide as antifungal, when and how should I transition them to tank water? The tank water has higher pH, higher TDS, higher oxygen, and I’m assuming more bacteria.
2) You don't need to do water changes until after they start swimming around and eating. And if you have a filter in the tank, you can start doing water changes after a few weeks.
I normally start with a tank that has 4-6 inches of water and each day I add a couple of litres of green water and infusoria. This slowly increases the water level over a few weeks and once the babies are a couple of weeks old, they should be readily eating newly hatched brineshrimp. You can tell if they are eating the brineshrimp because they get orange bellies. Once all the fry are eating brineshrimp, you can start doing 10-20% water changes each day for a few weeks, then increase it to 50% each day.
In my tanks I would do a 75-90% water change and gravel clean the substrate every day, once the fry where readily eating newly hatched brineshrimp and microworms. The big water changes keep disease organisms down and help dilute any growth inhibiting hormones produced by the fish. You don't have to do water changes this often but I find the fish grow a lot faster with big regular water changes.
I had water holding tanks in my fish room and the water was always aged for at least a week before it was used in any tank. Most people can't do this at home but it does help if you can have some water sitting around so you can do water changes each day if required or wanted.
The water in my holding tanks was generally the same temperature and had the same pH, GH & KH as the rearing tanks. This meant I could do huge water changes on fry tanks and they weren't exposed to sudden changes in water chemistry or temperature.
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2.1) What is the GH (general hardness), KH (carbonate hardness) and pH of your water supply?
This information can usually be obtained from your water supply company's website (Water Analysis Report) or by telephoning them. If they can't help you, take a glass full of tap water to the local pet shop and get them to test it for you. Write the results down (in numbers) when they do the tests. And ask them what the results are in (eg: ppm, dGH, or something else).
If your tap water has a low mineral content and doesn't contain anything toxic, you probably don't need to use reverse osmosis water. However, if the water is hard (has lots of minerals) then using some reverse osmosis water with some tap water would make it more suitable for the Corydoras. These catfish naturally occur in soft water (GH below 100ppm) and a slightly acidic pH (6.5-7.0), but some species come from water with a neutral (pH of 7.0) or slightly alkaline pH (pH around 7.5). If the pH of your water is between 6.5 & 7.5, it should be fine for most Corydoras unless you are dealing with wild caught fishes, and that is unlikely with bronze Cories (C. aeneus). If you get wild caught fish, it will be written on the tank and they usually cost a lot more.
If you are using reverse osmosis (r/o) water and a clean hatching container, there shouldn't be any need to use an anti-fungal treatment because the water should be free of pathogens. I never used anti-fungal treatments in my hatching tanks and I rarely had eggs get fungus on them. The fungus that normally affects fish eggs is Saprolegnia fungus and it looks like white hairs sticking up from the egg. The white hairs are about 3-4mm long and quite distinctive. You could try hatching eggs without fungal treatment and see if it helps.
If you do hatch them in r/o water, you should wait until they are at least one (preferably 3) month old before trying to change their water chemistry by adding harder water to their tank. Then you only want to add a very small amount of new water to the rearing tank and don't do it more than a couple of times a week. Andy's suggestion of 5% every few days is about as fast as you want to try changing the water chemistry and I would prefer it to be no more than 5% twice a week until they are 6 months old. When they are older they can tolerate bigger fluctuation much better than small fry can.
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Any water with aeration will have a higher oxygen level than stagnant water. High oxygen levels can also raise the pH a bit and high carbon dioxide levels can drop the pH a lot.
TDS is painful
Most TDS meters measure anything dissolved in the water and this can be minerals like calcium and magnesium, but also algae, fine sediment in the water, and even tannins from rotting plant matter. I prefer to measure pH, GH & KH and leave it at that. You can usually lower the TDS a bit by doing water changes and gravel cleaning the substrate, and by having a clean filter in the tank. In my opinion, it's just too variable and measures too much stuff to give useful information. If it's used in conjunction with other tests like pH, GH & KH, then it's more useful, but on its own, a TDS meter is a fancy gadget that doesn't help as much as it should.
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Established aquariums are home to all sorts of awful looking things that make your skin crawl (literally). Fish live in a soup of microscopic organisms including bacteria, fungus, viruses, protozoans, worms, flukes and various other things. Doing a big water change and gravel cleaning the substrate on a regular basis, cleaning the filter monthly and wiping the inside of the glass down each week, will dilute these organisms and reduce their numbers in the water, thus making it a safer and healthier environment for the fish. However, it's best to use clean water (not from an established aquarium) in a breeding tank to reduce the risk of harmful pathogens getting into the tank and harming the eggs or fry.
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3. Food advice- thank you! I forgot to mention I was feeding vinegar eels in addition to BBS. My Infusoria experiment looked and smelled like a biohazard, so I haven’t fed them any of that. I will try again with your advice- thank you!
If you are feeding vinegar eels that should help. The biggest hurdle for baby fish in the first few weeks of life is getting enough food in every cubic inch of water. You want enough food in the water so the fry only have to move 1/4 to 1/2 inch to get something to eat. This is where reducing the water level helps, because it brings the fry and food closer together. However, the smaller volume of water can deteriorate much quicker and you need to make sure it stays clean. An air operated sponge filter helps with this. You use an air operated sponge filter so it doesn't suck the fry up and kill them.
If your infusoria culture turns black and smells like an open sewer at 7am, that is caused by no aeration. As the plant matter breaks down, it needs oxygen for good bacteria to grow. Without aeration, the culture turns black and becomes anaerobic (lacking oxygen) and makes everyone in the house freak out about who farted. All my green water and infusoria cultures have lots of aeration to stop this happening.
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4. I actually bought this whole tank, fish, plants, shrimp, etc from the LFS with about 3” of water and all its inhabitants included. I’ve had an H of a time with it. I bought a dozen CPDs and they all went through slow death, various issues, since November when I bought the tank. I also lost one of the adult Cory that came with the tank- fungus and white blotches. I did notice that the previous owner let a fish die in the tank—I actually found some rib bones. It had a betta in it at the LFS, but I didn’t take the betta home because I have no experience with them and fear they are difficult/prone to disease. So my question, is there a potential this whole tank is riddled with some disease? Should I just harvest the eggs and hatch them out in completely separate tank and try not to cross contaminate?
White blotches on fish is usually excess mucous caused by something in the water irritating the fish. It can be poor water quality (ammonia, nitrite, nitrate incorrect pH), or an external protozoan infection like Costia. Big daily water changes and gravel cleaning the substrate usually helps if it's a water quality issue. If there is no improvement after a few days of water changes, then add some salt to kill off external protozoan parasites like Costia, Chilodonella or Trichodina.
Bettas are no more prone to disease than any other fish. They are heavily inbred and that has made them physically weaker, but they usually have fewer diseases because they are normally kept alone and don't get exposed to lots of new diseases from other fish.
As for the tank being riddled with disease, any fish tank that has fish in for more than a few months, will be riddled with diseases. As mentioned above, aquariums are a cesspool of microscopic organisms and most fish sold in shops are infected with something. If you are concerned about something bad being in the tank, do a 75% water change and gravel clean the substrate every day for a week. This will dilute most of the disease organisms in the aquarium and provide a cleaner place for the fish. Then do a 75% water change and gravel clean once a week after that.
Make sure any new water is free of chlorine/ chloramine before it's added to the tank.
Breeding the fish in a clean, freshly set up tank containing new water is generally the safest way to go if you want to reduce the number of disease organisms in the water. However, diseases and parasites can hide in plants and ornaments so these should be rinsed before being added to a breeding/ rearing tank.
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5. Yesterday the adult pair laid 125 eggs. I took out 25 infertile eggs today, leaving 100 potentially viable. I can see the wigglers moving inside the eggs. So exciting! Seems like a very successful mating so far. I usually lose them about 24-48 hours after they first hatch. Any suggestions to get through this critical phase?
See above and try different things. Eventually you will work out what is causing the problem and then things fall into place and you will be overrun by baby fish
If your local shop doesn't get bronze Cories in normally, ask them if they can order 6-10 in for you. Shops have a number of suppliers and usually carry what sells. Some shops carry a few unusual items and others only carry bread and butter species (guppies, neon tetras, angelfish). But they all have access to a wide variety of fish and most shops will order in fish for you if you ask nicely. You might have to put down a deposit and I would suggest being at the shop when the fish come in so you can check them as they come out of the box. You can then get the shop to re-gas the bag (with oxygen) of fish and take them straight home, or let the shop put them in their tanks for a week before you take them. I don't recommend taking the fish home if they have been in the shop tank for a couple of days. The fish suffer a lot of stress when being shipped and put into different tanks. So giving them a week in the shop tank before you take them, gives the fish a chance to recover from the first journey before they go on the next one to your place.
You should also try to avoid buying fish if they have just had a water change done or had one in the last couple of days. Water changes can stress new fish (especially if the water chemistry is significantly different) and letting them recover for 4 or 5 days after a water change will usually give you better results.
