To carbon or not to carbon

Hi all,

New Aquarium owner here. I had started up my 25 gal freshwater fish tank and conducted a fishless cycle for two weeks, I then introduced three flame tetras to help with the cycling process. A week later I added 3 more tetras and a pleco. I have no intention of adding more until I know the tank is cycled. I have been performing a 15% water change every few days, approx a week after adding the new fish I conducted a 15% water change, the next day they all had ick (definitely not bubbles from the water change, as nothing else had bubbles and the fish were getting worse). I went out and bought API super ick cure and followed the instructions on the back. The first step was to remove the carbon from my filter cartridge (I have a Top Fin 30 hanging filter), I removed the carbon and placed the cartridge back in. Gave the tank the first dose of ick cure and continued with the rest of the steps. Now the ick is gone and I performed a 25% water change. The instructions state that I should replace the carbon. What I didn't think of at the time was to save the carbon and add it back in... unfortunately I threw it out.

I have several questions:

1. Should I add new carbon?
2. Could I just replace the whole cartridge, will this throw the remaining good bacteria that clung on to the cartridge foam and frame?
3. Do I even need carbon would the fabric pouch suffice?

PS. I do not have the numbers of the chemical balance and cannot verify if the tank is cycled. I will have to take a sample in soon.

Thanks in advance,

Noel

Hi Noel,
Welcome to the forum!

It's great that you took the time to cycle the tank and I assume that the fishless cycle included using a source of ammonia for development of the nitrogen bacteria. Unless you had plants or snails in the aquarium, you may have been just cycling old water. The biologic cycles require sources of carbon, nitrogen and other trace elements, so for the nitrogen cycle to begin, you would need to add either old filter material from another tank, living plants, snails or used gravel.

After two weeks, normally the nitrogen cycle may be adequate to support your small load of fish. Unfortunately if you bought your fish from a LFS, many of them are stressed or recently brought from wholesalers. Unless they had been quarantined at the fish store for at least 7 days, they may have been carrying the disease or be vulnerable to ich. So the reasons why your fish developed ich is most likely because they were already sick when you purchased them. It is always good practice to ask if the fish were quarantined, or at least observe the fish store tank for at least seven days to see what develops. At lease your patience will guarantee that you will choose stronger fish and those without disease.

Adding medication usually wipes out the nitrogen bacteria which may have started so you will be back to restarting the nitrogen cycle. Definitely keep doing the water changes.

In answer to your questions:
1. Carbon is used to absorb toxins and chemicals. Since you are replenishing the water, you are doing the work of carbon so there is no need to replace the carbon while your are water changing. In fact, I have not used carbon for years. After a month of water changes, you can add carbon, if you wish.
2. Keep the whole cartridge. It is accumulating bacteria that will begin the biologic filtration.
3. The way I practice fishkeeping I rarely use carbon. I always us a filter media, and so the fabric pouch with filter media is sufficient.

Happy fishkeeping!

I'm with Alex on this; carbon is over-rated and usually unnecessary. I usually have some on hand in a tightly-sealed container in case I feel the need for it, but it's been years since I have actually used any. Whatever carbon will do...water changes will do at least as well or better.

When I did use it, I always utilized a small cheapo corner box filter, with just enough filter floss beneath and above the carbon to keep it contained.

And, when I used power filters a lot more than I do now, I always threw away the cartridge and modified the filter so that all the room that was designed for expensive, buy-some-more carbon and disposable floss was instead filled with open-cell foam cut to fit. Clean this when needed in old tank water that is about to be discarded...you know, from one of the all-important water changes...and you will never lose the culture of helpful bacteria that keeps your nitrogen cycle chugging along...and you will save a ton of money in the process.