Dying plecostomas

Question
QUESTION: 3 years, 75 gallons, all peaceful, 20, emperor dual bio wheel and a magnum, 6.8ph, monthly, approx 16.

I had a pleco for almost 3 years and it died. I have purchased replacement plecos and they all seem to die within a couple of weeks. I think it has been 4 replacements now from different suppliers. The tank is now starting to show considerable algae growth and I'm at a loss. I purchased a chinese algae eater and it doesn't seem to be able to keep the tank clean. All the other fish are thriving with no issues. Any help would be greatly appreciated. Thanks so much in advance.

ANSWER: Hi Robert;

Pleco deaths can be from dirty gravel, bullying by other fish, chronic high nitrates and, strangely enough - from starvation. There are many algaes that algae eating fish find distasteful or indigestible and some algae is just too hard for them to scrape off and eat.

What are the symptoms of the dying plecos, if any?
Do their bellies seem sunken?
What kind of algae is it? Color? Texture? Is it easy to scrape with a pad?
What is the nitrate level in the tank water?
How often do you vacuum the gravel?
Do you have a lot of decorations in the tank that could have waste under them?
Sometimes a pleco will root around the decorations and get his gills full of toxic gasses out of a dirty area of gravel. It can cause instant death or illness that leads to death.

Let me know what you can and we can go from there...

At Your Service;
Chris Robbins

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

QUESTION: Chris, No symptoms really. Alive one day and dead the next. Their bellies seem fine. The algae is greenish brown and fairly easy to remove just by wiping. I'm not sure about the nitrates I'm not sure I have ever tested that. Is there a special procedure or test kit for that. Some decorations but not too many. I vacuum each month with the water change.

Answer
Hi Robert;

I would make more frequent water changes and vacuum the gravel more often. Plecos need very clean gravel to thrive and all tanks really should have a 25% water change and gravel vacuuming once a week, every week anyway. Plecos spend a considerable amount of time near the bottom and maybe it's just not clean enough for them. It's worth a try and your other fish will have improved immune systems and better long-term health as a result.

Something else worth a peek at is toxic spots in the gravel. It just happens before we know it. I've seen cases where the a pleco will try hard to get at algae under the edge of a rock or something and comes into contact with a small area of the gravel that has collected rotting waste under it. A few bubbles of toxic Hydrogen Sulfide gas goes over their gills and they die. Sounds weird but it happens sometimes. If the problem continues, the toxic gas could affect the rest of the fish. If you get bubbles of gas up the gravel vacuum tube in some areas, take a handful of the gravel from that spot and do a "sniff test". Just take a smell of it. If it smells like rotten eggs, even just a little bit, it's hydrogen sulfide.

There are some tanks too that just don't support certain species of fish for whatever reason. The chemistry seems okay but they just don't survive in it. Just a mystery in some cases....

At Your Service;
Xhris Robbins