Pipework can be simulated with various thickness wire, for instance mains electricity cable for wiring homes comes in .5, 1, 1.5 and 2mm thickness if you strip away the insulation from the copper wire - it can be thicker if you leave the plastic insulation in place, but then it is more difficult to get a sharp bend in it. Once painted you will never tell the difference between it and plastic tubing.
A tip for your pipework, draw the pipe runs on a seperate piece of board that can simulate your deck, bend all the pipe on to that diagram and when you are happy with them, its just a case of transferring the pipes to your model deck.
If you look at the weathering paints by Vallejo, AK or Mig, you will find a suitable acrylic algae for weathering, one bottle will cost around 3€ and will be more than enough for your ship. If you want a thicker algal growth you can mix in some of the powder sold for model railways to simulate trackside grass, but that stuff is expensive for a bag full when you will only need a small spoonful. I've seen in the diorama pages on facebook that they also use cooking herbs, that might work if given an overspray of matt clear varnish afterwards.
Your model detail is superb as usual, can't wait for the next update.