Pleco not eating

Our large Pleco stopped eating at least 14 days ago. We're not sure of his age,we've had him for about 2 yrs and he was large when we got him.
This not eating just happened suddenly, one day he was fine,one day not.
He's in a 240ltr tank. His tank mates are 4 x Congo, 5 scissor tail, 4 rainbow tetras, 4 silver sharks, 2 Corydoras, 1x4" Bristlenose, 1x5" Pleco & 1x Featherfish Catfish (super placid). There are no aggressive fish in this tank.
In the 1st picture, you can see the 'poop' he's been doing. He's been in this corner, not moving since he's been unwell. Just before he got unwell, we noticed this white are on his head, which we initially thought could've been a heater burn, but it went away. (Pics 4&5)
The water parameters are,
PH - 7.6
Ammonia - slightly over 0 ppm
Nitrite - 0 ppm
Nitrate - 160 ppm (how do I get this down)
Other fish are all good!
Water change, substrate vacuum and filter clean was done 14th Jan..
Any help would be greatly appreciated.

You need to ramp up your water changes schedule and change more water. A lot more.

start with 50% per day if no sign of stress appears. do that for a week.

Then change more than 50% per week.

Your nitrate reading are 3 times the tolerated level for scaleless fishes. And at least twice the general maximum common fishes will endure.

Scaled or scaleless, it doesn’t really matter. High nitrates are toxic to all fish, and every species has its own tolerance level.
Nitrates should literally be kept as low as possible. That’s the main reason we do weekly water changes.

Fish that stop eating due to high nitrates often never eat again, as the damage is already done, but get them down ASAP for the sake of all the other fish aswell.

Thanks for your replies... Yeah, I realised the Nitrate levels are way too high...
Christmas eve I did 25-30% changes in all of our other tanks (because we had the extended family coming and they were due) and used the last of my chlorine neutraliser... Obviously they'd put a lot into the water to last the holidays and I lost a whole heap of my Guppies in the time that the aquariums were closed. I had the same thing we're all levels were good except the Nitrate levels. We did a water change on this tank last weekend.
Our water change schedule depends on the particular tank and the fish load, and this particular tank normally gets a 50% done every 2nd week. But it was longer this time because of what happened before Christmas...
I'll do a 50% tomorrow, but is there anything that can be done to help beforehand?

Kessafan said:

I'll do a 50% tomorrow, but is there anything that can be done to help beforehand?

Click to expand...

No, nothing.

Obviously this tank needs more than 50% a fortnight. Use the nitrate level to tell you how much you need to change. You need to get it down close to your supply-water level every week. I would be doing at least 50% a week... possibly twice a week. 240 litres is a tiny tank (too small) for such a large plec. Not to mention the Bala Sharks that grow just as big.

We've only been having Nitrate issues since Christmas and this particular tank was 1 of 2 that didn't have a water change on the 24th Dec... and the ones that were changed had the high nitrate spike that killed a lot of my Guppies. This tank was only changed recently (2 weeks) and up to then has been running for over 2 years with no issues.

You have too many plecos in a tank that small...36ish US gallons. I would strongly recommend removing this one as well as the Bala sharks that can get to excess of 8" as adults. One of those fish I don't think stores should be able to sell.
To remove 160ppm nitrates you will have to do multiple large WC which will stress your tankmates but needs to be done.

A 50% may reduce the nitrates to 80 , then another 50% WC to 40, and rinse and repeat until your as low as you can get. I have done 60-75% WC on my tanks in the past but with healthy fish. Your fish are more likely super stressed from the high nitrates so a large WC could add to the stress. A series of smaller ones say twice a day until you get the levels down is recommended.