but i simply cant tell because i never see them eating.
I agree with lilfishie in that you may not only be able to see your pleco(s) eat more often by providing food just before 'lights-out', but would add that this may also help ensure that your pleco(s) have a better shot at the food before the other fish in the tank, if any, eat it. I have also enjoyed watching my plecos after lights-out with the aid of some moonlights and would add that having the tank lit, albeit dimly, may prove to help your pleco(s) become more acclimated to being active during the day time hours -- although I doubt that this 'trick' would work all of the time so "your results may vary"
So it is by far the better option to research the individual plec than make generalisations about plecs as a whole which amounts to nothing of any real value...
Please take no offense to this, but I would have to disagree with you for the exact same reasons as I already explained....while most, if not all plecos I have read/heard about are omnivores, many of them will be primarily herbivores when first starting life but 'switch' to being more of a carnivorous omnivore later in life. Why is this something of great value (IMHO anyways) is because we may be doing a great injustice for our plecos if we simply assume that they will be 'herbivores for life'. In fact, even though I haven't tried to refresh my memory yet, I wouldn't be too scared to say that a very vast majority of the more commonly kept pleco species (e.g. common plecos, bristle nose, rubber/bull dog, etc...) are relatively apt to change dietary preferences like I am suggesting. To further support that notion, I have read in more than one place that starvation is arguably the most common cause of death in plecos (and probably most 'algae eaters') so if we hope to avoid that fate, we should understand that a pleco's dietary needs are not always black and white. For further support, I am sure that anyone who spends some amount of time in the hobby, and especially on forums like this one, will eventually hear about someone complaining or asking questions about why his/her pleco was found 'sucking' on the side of a tank mate, or even caught eating a dead fish, if you haven't already. Granted, I would tend to believe that a pleco would be very low on the suspect list of possible causes for the death of another fish, they are often times very willing to eat it.
Lastly, I think it is prudent to point out that, in many cases, we purchase plecos without knowing exactly what type it is since some are hard to differentiate between when they are young -- which, I am sure that if you look hard enough, you will find at least a handful of people who were amazed to see his/her bristle nose pleco (one of the smaller plecos in case anyone didn't already know) grow to nearly a foot long because, as it turns out, it was mislabeled in the LFS. With that in mind, it becomes slightly more valuable to have a decent grasp on the diet of plecos in a more general sense.
...besides, as we speak about regarding most every other fish, plecos can benefit greatly from a varied diet. <=== which is valuable in a myriad of ways
Don't get me wrong though....I should have prefaced my initial comments by voicing my opinion regarding the purchase of any fish/invert in a freshwater tank solely to perform some sort of 'job' as being a mistake in most, if not all cases since we can do the same job ourselves with relative ease. With that in mind, I do agree with the notion that, if keeping a pleco because you actually want (versus need) one, it is best to do the research on that specific species ideal diet. So, to clarify, I agree with you Darkstar, but only find value in information/ideas that you may not.
