Within the next week or two, I will be building a raised pond for gold fish but have a few questions.
The pond dimensions, finished and filled will be 4m x 3m x1m deep (12000 litres excluding filters).
Filtration will be aerated retro fit bottom drain,8500lph pump fed to nexus easy pod then 4" gravity return to pond.
The second part of filtration will be skimmer to modified multibay filter to pond.
1st question is regarding the skimmer, would it be best to pump feed from the skimmer to the multibay and gravity return back to pond or gravity feed from skimmer to multibay then pumped water returns below the waters surface?
Will be a UV on skimmer line and also on easy pod.
2nd question, what would be an acceptable stocking level?
Honestly I don't know much... though I built my own pond, but all of my big tanks + pond has DIY filtration system instead of commercially produced ones. So I will try to answer with my experience.
1. For skimmer and filtration, Usually I prefer to gravity feed to the filtration chamber (or maybe multibay if I understand it correctly). - If you do gravity feed, you can ensure that even if the pump breaks down or whatever, water will still be kept inside the chamber due to gravity and keeping the bacteria alive. Keep in mind that bacteria requires oxygen too to live. That's why I always design the filtration chamber with decent surface area. - But either as long as water flow through everything, it should be working.
2. For stock level. - If you keep normal goldfish, I think you can have around 20-25 of them (Base on the idea of approximate 50l per goldfish) - However I strongly recommend to start with 10-15. Check your nitrate level after 2 weeks then again in 1 month. If it's still managable with water change then you can add 5-10 more. But make sure to have no more than 25 or there will be too few space for them to swim. I think 20 would be okay.