First lets discuss the nitrate level. They are border line and the lower you can keep it the better. For a planted tank, you do want some nitrate but usually no more than 10ppm. There are few things you can do to both lower nitrate and reduce algae growth.
I would recommend you do a 10% water change twice a week for the next couple of weeks. Keep feeds at a minimum of two minutes per day...but only three days out of the week until nitrate levels come down some. Retest nitrate weekly to keep tabs on any progress. Once nitrate levels are lowered then return to a normal feed routine as discussed earlier.
Add more plants. Plants are a natural competitor of algae; feeding off the same nutrients.
You can also use a denitrate absorber in your filter. A good medium to put in there is Phos-X by Hagen. It will help reduce nitrates, phosphates, and in turn help control algae.
BTW...what kind of filter do you have?
HOB? Canister? Undergravel? (Please don't say undergravel).
I don't know all the names to all the different types of algae. I see that it's green and is common on glass, but not necessarily
cyano. Cyano is actually a type of bacteria. Controlling nitrates will help control all types of algae.
There are three contributors to algae growth in a tank...light, nitrate, and phosphate. If you get the chance, see if your
LFS would do a phosphate test. Phosphates are common in tap water. It's used as a anti rust agent in city water pipes.
Do you have any sunlight hitting the tank?
You don't have a big problem, but you can be on the verge of one, so it's best to get on it now, than to wait till it is a problem.
Know what's cool to have?
FW clams and large flower shrimp. So long as you've never treated the tank with copper based medications, they can make unique additions. The clams are short lived and thankfully fairly inexpensive, but they eat nitrate. The flower shrimp are neat. They can reach about 4" and they don't have claws. Instead they have these flower like appendages on their front arms that open and close to catch minuet particles and collect algae to eat...hence 'flower' shrimp.
Now the algae eater issue...
It's possible that the fish he was eating the slime off of was sick whether you knew it or not or the pleco wasn't getting enough food elsewhere.
In my 20+ years of dealing with animals of all types, I've never seen a pleco go after a healthy fish unless it was starving. It is very easy to go without notice. Plecos are bony to begin with and fairly difficult to see them thin out from lack of food. Once these animals are fed well, they leave healthy fish alone, including slow rolly polly fantails...
LOL.
Plecos have a largely vegetarian diet with some meat from the occassional carrion and sick fish. Vegetable protein isn't as rich and concentrated as meat protein, so therefore vegetation eaters require a lot more food. If you give a fish that is naturally a vegetation eater a rich meat protein diet, it can make them very ill. It can constipate the fish then they can't pass their waste. It can kill then if left untreated. So you want to provide more vegetation matter.
Best time to feed them is when the lights go off for the night. I personally think feeding them strips of algae or romaine lettuce, cucumber and zuccini is a lot cleaner for the tank than algae wafers, more nutritious and fills them up better. They REALLY like the zuccini and cucumber and beefs them up good. By daytime, what ever remains in the tank, take out. It's also good to have driftwood in the tank for plecos. They eat a fungus that grows on the wood that helps aid their digestion. Some species, it is absolutely required like the sensitive zebra pleco which specializes mostly on feeding off of dead things. Carrion is a requirement in their diet actually (yuk). Glad you're not a scavenger?
LOL.
I have seen other types of catfish eat a fish's slime. I once had a synodontis cat that I found after going through three clown knives, was eating on them...and he was not starved...but then again...he wasn't a pleco. Synodontis cats are carnivores; not vegetation nor omnivores. Chinese algae eaters are perhaps the worst when it comes to attacking other fish. This is natural behavior for them as they mature into adults. I only recommend them for African cichlid tanks and tanks with fast fish like minnows and rainbows.
Otocinclus are small and perhaps a curious goldfish might take a try at them, but they are so barbed; they stick to things like velcro. Ever catch one in a net? They're just as bad as pictus cats. The goldfish would have difficulties...
LOL. And their fins are sharp and very pointy. They are like daggers. For tiny fish, they're well armed. This doesn't say they don't get eaten, but for a goldfish that have no teeth to grab hold, it wouldn't feel good...
LOL.
Good luck on your exams. What are you studying?
