Cloudy green water; fish dying

[PizzaAndPopcorn]

Hi! We started a new 20 gallon tank 9 weeks ago using some water from a previous betta tank. After 2 weeks, the tank was cycled (0 ammonia, 0 nitrites, 5-10 nitrates). Next, we added 3 guppies, 2 gold panda mollies, and 5 cherry barbs. About 10 days later, the water turned cloudy and green, and several fish died. The water cleared up after a week, but after a month the water is cloudy and green again and another fish has died. We have removed all of the fish and put them in a separate tank, which has not displayed the same problems of the 20 gallon tank. Our questions are, why is the water cloudy, what could have caused the fish to die, and what do we do now?

Additional information: This 20 gallon tank has an Aqueon LED QuietFlow 10 filter (we removed the supplemental ammonia cartridge after a month). We use an API Master Test Kit and have not had ammonia or nitrites in the 20 gallon tank while fish have been in the tank. Our average weekly water change is 2 gallons (10%) and we vacuum most of the gravel with each WC. New water (tap) gets treated with water conditioner and bacteria supplement. We had the LED lights on 12 hours a day for a while, then we turned off the aquarium lights to decrease risk of an algae bloom, but another bloom happened anyway. We are using white gravel, which we rinsed many times until water was not cloudy anymore. pH is 7.8. Temperature is 76. Latest nitrates was 20 ppm.

 

[Kame]

Does your tank get hit by direct sunlight?
Does your tank contain any plants?
Definitely reduce your lighting time, I would reduce it to around 6 until you get the algae under control and then move it up to 8-10 over time as it gets better. 12 hours is especially long if your tank does not contain any plants as the algae has nothing to compete with. Also ensure that you're not overfeeding your fish as that can contribute to the problem.

I would upgrade your filter as well, Aqueon advertises it as doing up to 20 gallons but that's really pushing it. You generally want a filter with a turnover rate of at least six times your tank's volume, which would mean a filter of atleast 120 gph, that aqueon is 100. Most filters perform under what's advertised and even worse as they age, something to keep in mind as poor filtration can easily be a contributor to your problem.

Oh also, I would increase your weekly water change to 20-30%.

 

[PizzaAndPopcorn]

Kame, thanks for your reply. The tank receives no direct sunlight and contains no plants. We reduced the tank light time already. Thanks for your insight about the filter, especially the detailed numbers supporting your recommendation; we will definitely look at replacing it.

About your recommendation to increase the weekly water change by 20-30%, is there a goal (X ppm nitrates, etc) that we should be shooting for? I thought we were OK as far as nitrates go. We have not come close to 40 ppm.

 

[Kame]

Keeping it under 40 is what I hear from most sources, but most fish are pretty tolerant of nitrate.
I suggest larger water changes since you're having these algae problems, 20-30% is a good idea to help remove any excess detritus that may have built up while gravel vacuuming as well as reduce any nutrient buildup like phosphates that may be occuring due to feeding. 20 ppm nitrate seems high to me for a tank that has no plants or active substrate, which would lead me to think that your tank may need deeper cleaning/better filtration or that your water changes aren't large enough to outcompete the nitrate build up.

You said you reduced the lighting time, however, if there is still currently a bloom in the water I would suggest blacking out the tank entirely until the bloom is under control & try some of these suggestions to see if they help.

 

[Fishkeeper88]

If you are using the Ammonia reduction filter media.

You might be hiding huge Ammonia and Nitrate spikes and getting miss interpreted reading when you test your water. I highly recommend all people no matter the tank not use these as they buffer and dampen the true nature of anaerobic and aerobic bacterial filtration. All aquariums contain Natural bacteria that eat junk. This bacteria cycle is what eats Ammonia and Nitrites producing Nitrates. Nitrates then only leave the aquarium during a water change. If you are using this Ammonia reducing filter media anyone... Remember get rid of it and replace it with layers of 1. filter foam, 2. Charcoal Bag, 3. biological filter pellets in a filter bag. I even sometimes just use foam and a huge bag of biological pellets.

Also it sounds like both an algae and bacterial bloom. Please get yourself a UV Filter tube sterilizer and pump or replace the substrate, decorations and filter. This micro algae is especially minute in size. It will cling and replicate on surfaces. I recommend just getting a UV Sterilizer and replacing the filter with a better one such as an Aquaclear by Fluval Hang on back.

UV Sterilizer https://www.petco.com/shop/en/petco...nh-B8czH7VqAbSJnIdhoCmRYQAvD_BwE&gclsrc=aw.ds

 

[PizzaAndPopcorn]

if there is still currently a bloom in the water I would suggest blacking out the tank entirely until the bloom is under control & try some of these suggestions to see if they help.

Thanks. We did black out the tank a few days ago. The water now is still green, but less cloudy now. Any thoughts about how to salvage what we have or start over? There are no fish in the tank. Should we keep a percentage of the water in the tank and add more or start over?

 

[PizzaAndPopcorn]

Also it sounds like both an algae and bacterial bloom. Please get yourself a UV Filter tube sterilizer and pump or replace the substrate, decorations and filter. This micro algae is especially minute in size. It will cling and replicate on surfaces. I recommend just getting a UV Sterilizer and replacing the filter with a better one such as an Aquaclear by Fluval Hang on back.[/url]

Thanks for the advice about the ammonia filter. We got rid of that early on.

Also, we now have a small white blob growing in the gravel.

A UV sterilizer looks like a pricey investment. Since we don't have fish in the tank, we could just start over, using some water from a stable tank, right? I'm assuming we should rinse the gravel and wash all of the decorations?