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Freshwater Aquarium/75 gallon aquarium water cloudy (hazy)


QUESTION: Hi I am fairly new to keeping freshwater aquariums (started 4 months ago) and I have a freshwater 75 gallon aquarium that I just had to break down and setup again due to an issue with a possibly contaminated bag of carbon that I purchased (lost half of my fish due to it). It has been only 2 days since setting it back up and the water in my tank is already cloudy (hazy).

I do not overfeed, schedule is 2x daily but only what they can eat in 1 minute. I run a Marineland c-360 filter containing Marineland carbon with ammonia reducing white diamond, standard filter floss, and purigen (filter also contains typical bio-balls, ceramic rings and a polishing pad). I use Prime on the water just for the slime coat (I only use RO water in my tanks) and I also seed it with the Seachem Stability. I use small gravel substrate (washed very well). Have a bubble wall and a Marineland maxi-jet pro 600 in the tank as well.

Fish stocked at this moment are:
2 Turquoise Rainbowfish
3 Dwarf neon Rainbowfish
1 Australian Rainbowfish
2 Congo Tetra
2 Bushy Nose Pleco
1 Golden Wonder Killifish
1 Powder Blue Dwarf Gourami

For a total of 12 fish (not full adult size yet most are babies). These are the fish that survived the 'incident' and had to go back in the tank right away once setup.

Water parameters are as follows:
ammonia 0
nitrite 0
nitrate 0
ph 7.2

*FYI: the water in my 75 was finally crystal clear right before the possible contaminated carbon incident but took over a month to get there.*

I have another tank that is a 29 gallon, just recently upgraded from a 20 gallon and that water is crystal clear still.

Please help me with the cloudy (hazy) water issue. I'd like to know the reasons why it happens and how you can correct it.

Thank you for your time, I appreciate it. Please let me know if you need any additional information.

ANSWER: Hi Trish

When you broke down the tank and set it up again, you killed the beneficial bacteria that was in the tank. I'm not saying what you did was wrong, it's just that the tank has started the cycle process all over again. The cloudiness you're seeing is a bacteria bloom. It will clear up on it's own, but it will take some time. During the cycle process, you'll need extra water changes, about 20% twice a week.

Here is a link to further assist you with cloudy tank water....

Hope this helps you, good luck!


---------- FOLLOW-UP ----------

QUESTION: Thank you for your quick response Richard. May I ask you another question?

Have you ever heard of carbon killing fish? I can't write the brand name here in this email, but I can say it is well known and they have been around for many years.

This is what happened. After doing only a 15% water change (the weekly usual) I placed this 'carbon' into my filter after lightly rinsing per directions. (Also as I was rinsing it with RO water I noticed what was coming from it looked black like ink and even stained my hands! I was not certain that this seemed right, however I did proceed to place this product in my filter). This was the only change that I made (never used the product before). By the next day I was losing fish. They would swim quickly and erratically and then flip upside down. I immediately would take them out and place them in my hospital tank. They would last a little while and then die. I was making tons of phone calls trying to figure out what happened and what to do (even called the 'carbon' company!). However, most pro's told me to just keep watching them and do small water changes daily. I noticed that my tank looked very grey. I decided to go against what they said and pull the remaining fish and put them in my hospital tank with fresh water. I broke the tank down, threw out the substrate (was wanting to switch anyway) and cleansed everything with vinegar/water mix and then rinsed, rinsed, and rinsed before putting it all back together again. There were some ornaments that I needed to throw away as it appeared they had been stained/tinged by the 'carbon'. There was also a coating of powdery like stuff you could see coming off of the ornaments and fake plants as we were taking them out of the water. Well, thankfully my remaining fish that I pulled out all survived and they look happy and healthy now.

My tank is setup now just like I had it before I placed the new 'carbon' into my's sparkling clean and crystal clear.

Please let me know your thoughts on this. I would like to know if anyone has ever experienced anything similar to this before. Also, what was happening to the fish when they were swimming erratically like that? One person said they were having mini-heart that true?

Again, thank you for your time and knowledge, it is much appreciated.

Hi Trish

I apologize for the delay in answering your question. I had a lot going on and forgot to mark myself "away" on the site.

I've never heard of carbon killing fish or leaving the residue that you described. In speaking with a couple of other experts on the site, they've never heard of an experience like that either. I use the carbon packs in all my filters, not loose carbon. I wouldn't purchase that brand again.

Usually when all fish in the tank are swimming erratically, it is because there is a problem in the tank, more often than not, high ammonia levels. Temperature shock, pH shock, high mineral content, and residual chlorine will also cause this behavior. Always use a high quality water conditioner such as StressCoat or Aquasafe.

I'm glad your tank is back to normal and your fish seem happy and healthy. Keep up your tank maintenance and test your parameters regularly.

Hope this helps, good luck!


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Richard Hight


I own and maintain several freshwater aquariums from 2 to 180 gallon. I can answer most questions about freshwater aquariums, including setup, cycling, maintenance, compatible tank mates, feeding. Moving? I've moved fish both across town and across the country and can help you get your little aquatic friends to their new home safely. I know and have experience with most freshwater community fish, South American Cichlids and African Cichlids. I don't answer questions about Goldfish or keeping Goldfish with Tropical Fish. I also don't answer questions about keeping crustaceans (shrimp, snails, crabs etc) with Tropical Fish, nor questions about saltwater fish or aquariums. I'm not available to answer questions on weekends, this is when I do maintenance on my own tanks.


Many years of personal experience with community tank fish, semi-aggressive fish (Barbs, Tetras, etc), Angels, South American Cichlids and African Cichlids.

HSG 2010-2011 prof

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