Mysterious Deaths and Controlling Nitrate Levels

jpostit

New member
Hello,
This is my first time posting to a forum for help (yay!).

Background: I have a 60 gallon tank which is the upgrade from my 46 gallon I had set up for 1 year. I set up my 60 gallon and was able to use the same canister filter and decor I had on my smaller established tank, so the cycle process was pretty easy. I had 8 fish (7 Mbuna African cichlids and a pleco). I set this tank up in April (4 months ago). I hadn't lost any fish in the transfer and one of my fish actually started holding and a few weeks later I found several fry swimming around. I do a 15 gallon water change every week and I clean the canister every third water change. I rinse all the media in aquarium or treated water. I test the water weekly using both API strips and the API master test kit. I have a digital thermometer and a floating one to ensure the temperature remains constant. I feed the fish a small amount 2x day and nothing is left over or even makes it to the bottom. In the canister I have a mechanical filter (black sponge) --> Purigen--> carbon --> bio media. My water tests have been consistently the following:
PH-7.5-8
Ammonia: 0-.25ppm
Nitrite: 0ppm
Nitrate: 40ppm

Issue: I went on vacation for 1 week and did a water change right before I left. I had a house sitter that fed the fish 1x per day and I rationed all the food out before I left so they wouldn't get over fed. When I returned there was noticeably more brown diatom algae on the rocks and decor and the pleco was nowhere to be found. Upon further inspection, I found the pleco dead in a plant. Its body had not turned white yet and there were no signs of injury so it was definitely very recent. I did a water test and everything looked normal. The next day I did a 15 gallon water change and scrubbed all the decor in aquarium/treated water. My female demansoni looked like she was holding again and was refusing to eat and hiding more (normal behavior when holding). 5-6 days later she was in a strange spot in the aquarium and not quite acting like herself. The next day she was dead and had clearly been picked on by the others. I promptly, did a water change and cleaned the canister filter. I started using Purigen about 6 months ago and had just replaced the packet about 4 weeks ago. However, it was more brown or discolored than normal. When I was cleaning the tank the day after the demansoni's death, I found a fry- so she was holding when she died.

Without any visible signs of injury or disease and my ammonia & nitrite levels being ideal, I am not sure what caused the death of these fish. The diatom bloom and discoloration of the Purigen packet make me think Nitrate poisoning or shock might be to blame. I read that plecos can be sensitive to that but people also say they are very hardy fish, so I don't know! I tested my tap water that I put into the tank and the Nitrate level in the tap is 5ppm. I don't understand why with consistent 25% water changes and Purigen that I can't get the Nitrate below 40ppm. Does anyone have any recommendation for how to lower my nitrate levels or what else I can do to prevent more fish from mysteriously dying? I have thought about using medicated food to treat for invisible parasites but again, I haven't seen any white poop, sunken bellies, or noticeable signs of disease. I even tested the phosphate and silicate levels which were 1mg/L and 4mg/L respectively.

Thanks in advance for your help!
 

OB Guy

Administrator
Welcome to Cichlidaholics. Nice looking fish and aquarium. What kind of filter are you running on the tank?
 

jpostit

New member
I currently have a 24W UV Sterilizer and a Penn-Plax Cascade canister filter model #1500 (rated for up to 150g).
 

OB Guy

Administrator
How long do you have the light on per day? Any chance the house sitter left the light on? That could explain the diatoms. As far as the high nitrates go I'd consider feeding the fish once a day or bump up to 50% weekly water changes. Less feeding will also help get rid of the diatoms.
 
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