those three are all safe to use in tropical tanks

I regularly do 75% or more water changes on my ancistrus grow out tanks. The idea that a water change of 40% would harm the pl*co is simply untrue unless the water parameters in the tank had greatly shifted from infrequent changes prior to that. of course,but the way she said it was that she had a ...

hmmm maybe,but plecs arent usually too sensitive with malachite.
Please correct me if im wrong

i think the offical stat is that most fish can go 3 months or so without food if they are healthy. In my opinion i would simply leave them to it for 10 days,the amount of people i talk to that have lost lots of fish because of people over feeding whilst they are on holiday is simply astonishing. My ...

if you only have plecs then in theory it can,just make sure youve got plenty of oxygen in there and you dont overdose and things should be fine. If you have any scaleless fish (loach etc) the dose should be halved,and i would think seriously about even using it :) seek other treatments for it such ...

to be honest you should never need to do a bigger than 20% water change,did you clean your filter out at the same time?and if so how did you clean it?
40% is a rather large change and its probably this which has upset him