Have today added our first fish to our Aqua Start 900. We have 8 cardinal Tetras and 6 zebra Danios. The aquarium is planted with real and plastic plants, bogwood, ornamental mangrove root and a small ornamental metal bridge. All going well and it looks beautiful! We have taken so much care to make sure everything is right - water testing, external pump and ensuring the temperature is correct, so we were alarmed to see a small amount of white mould on one of the plastic plants. What is it and what should we do? Is it dangerous for the fish? Thanks for any advice!