Algae Issues - Strings Of Algae All Over Tank!

So my light cutting down seems to have been doing the trick in that my tank has much less algae now! Good news, about that but less good news about everything else. Yesterday I bought a new Anubis and some RO water so I did my normal water change and added the new plant. Whilst doing the water change lots of black bits were ALL over the tank but unfortunately my gravel cleaner seems to be on its way out as it wasn't working properly. I have no idea what the black bits were - it surely couldn't have been waste as I only have three shrimp and 1 fish so I suspect it was algae breaking down. After the water change everything seemed fine and there wasn't any issues with my readings but this morning I woke up to a dead fish  Gutting as this little guy had been my only survivor and seemed so hardy and happy. The MA still don't have my killis in stock (I guess that's a good thing though since I lost my fish the day after) so now I don't know what to do. Since I don't seem to be having any luck with the killis maybe I should give up and get different fish, perhaps a betta. Though now I have the three Amanos so don't think they're suited tank mates. I do still have the killis on order. I don't know  I'll be buying a new gravel siphon to try and get rid of all the black stuff which could have been the cause of my killis demise. Difficult timing as I'm away this weekend so worried about my Amanos. I don't know what's going wrong with this fish keeping business 

Yes I did a 50:50 tap water to RO mix as I usually do so don't think that could be the cause 

If you'd done something horrible to the tank, the amanos would be trying to climb out, using any cables as a ladder. If they are still happily pootling round the water is fine.

It might just be that species of fish that is sensitive, or even the particular individuals you bought.

In that case I think the tank is fine as my shrimps were happily gobbling their way around the tank as usual. Such a shame about my little killi though. Guess I'll have a think and decide whether to try different fish or give them one more go when my MA order comes in

It might just be coincidence jesnon, was it old?

I hope so. He wasn't very old but I have had him a few months and his previous tank mates died so they could have been a sickly bunch of fish