Thanks for the replies
It's a 48L tank with x4 guppy's, x2 swordtails, x2 dalmation molly's, x1 blue ram, x2 peppered corydoras, x2 otocinclus and x2 amano shrimps. I haven't got a pH measure kit etc, (could do to buy). I've checked the temp - 23C/67F. Will try the water change tomorrow and add...