And just because you are having an ongoing unresolved issue does not mean you are doing it the worst way.
But something is not right, so I'm just suggesting to try something else.
I fully agree that a constant water change system is best, but it needs to be changing enough water per unit time for that to be true. I don't mean that massive changes are better; what I mean is that the quantity of water being changed per unit of time needs to be large, and even calling something a "drip" changer is a bit silly considering the size of your system. Changing 70% of your water in one big operation once a week will certainly be better than changing 10% or 20% through a constant "drip" system. In fact, in order to get the same benefits, your drip would need to change a larger total amount of water per unit of time than a single large change, because the drip is not changing out only "old" water but a mixture of old and new.
Individual large water changes are not the "best" way...but IMHO large-scale changes, however they are done (in single operations or through a constant flow-through system)...are definitely better than any wishful system that tries to make the same old water last forever. A "closed eco-system" would, by definition, require no feeding...and this would require, for your stocking level, an astronomical amount of vegetation growing in there. So if you accept that your fish will need food added regularly, I think you need to accept also that your water will need changing. No amount of algae scrubbing or UV-sterilizing or filtration will change that. I don't think you have ever explained exactly how much water your system changes each week, not going back through multiple threads to look again. Just mentioned turning up the flow as a possible suggestion to address your water issues.
Sorry if this has been a derail or if it sounds confrontational, and best of luck.

I fully agree that a constant water change system is best, but it needs to be changing enough water per unit time for that to be true. I don't mean that massive changes are better; what I mean is that the quantity of water being changed per unit of time needs to be large, and even calling something a "drip" changer is a bit silly considering the size of your system. Changing 70% of your water in one big operation once a week will certainly be better than changing 10% or 20% through a constant "drip" system. In fact, in order to get the same benefits, your drip would need to change a larger total amount of water per unit of time than a single large change, because the drip is not changing out only "old" water but a mixture of old and new.
Individual large water changes are not the "best" way...but IMHO large-scale changes, however they are done (in single operations or through a constant flow-through system)...are definitely better than any wishful system that tries to make the same old water last forever. A "closed eco-system" would, by definition, require no feeding...and this would require, for your stocking level, an astronomical amount of vegetation growing in there. So if you accept that your fish will need food added regularly, I think you need to accept also that your water will need changing. No amount of algae scrubbing or UV-sterilizing or filtration will change that. I don't think you have ever explained exactly how much water your system changes each week, not going back through multiple threads to look again. Just mentioned turning up the flow as a possible suggestion to address your water issues.
Sorry if this has been a derail or if it sounds confrontational, and best of luck.
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