Long-term scrubber usage

[Floyd R Turbo]

I had a thought while troubleshooting someone's build on RC (der wille zur macht). He is running his scrubber on a tank that is new, man made rock, etc. I think we pinpointed a couple issues regarding his scrubber not growing green, but rather brown/yellow and slimy, mainly those being too large (now smaller) and improper reflectors combined with not long enough photoperiod (as they likely aren't optimal for CFLs to mandate the 'double-light' rule) but it got me thinking about my scrubber. So I posted this:

I have noticed on my system that I am growing a lot of the yellow gooey stuff and messing with the photoperiod hasn't seemed to change very much, but my screen is still oversized as well. When first started the system, I got awesome green growth for months. When I moved the entire setup, and let the tank go without the scrubber for a week (on 2 separate occasions) the first few weeks to months of growth were awesome, and on each instance (move) the growth slowly progressed to a less green, more yellow type of growth. After the second move I trimmed the screen down at the same time, just to clarify. I am also locked into T5HOs for the lamp length so I lost a little effective intensity by trimming down from 20" wide to 14". But anyways, my point is that it might be possible that as you run a scrubber longer on a tank that has history without one (an established tank), it will take some time to suck out all of the N and P in the rock and substrate, and when that's gone, you are left with an even more oversized scrubber than is required.

I'm waxing a little philosophic here, but I think there is a point to be made with respect to Wille's tank - it has no history at all behind it, there's no N and P soaked into the rock for the scrubber to pull out on startup, so you may have skipped over the progression stage that I have seen and are now it a "food in, algae out" direct relationship. I might have to run this by a few others elsewhere to see if it makes any sense, right now it's just rolling around in my head. It makes sense to me because people that have nasty rock generally need a good 6 months of powerful scrubbing to get past the initial brown/black stages and into the green stage. The natural progression, all other factors being equal (feeding, no trapped dead fish, etc) is that the algae will eventually 'use up' all of the last remaining nutrients is needs to grow at the level it was before, and ends up going yellow. The solution would seem to be that you would start heavy feeding, or downsize the scrubber even further. If this ends up being the case, that means even the current feeding/sizing guideline would be too big for the long term, which would mean these systems are even better that we all thought.

I'm re-posting this section here because I have to wonder if there is any truth to this. It seems to make sense to me that as the nutrients (waste) available to the scrubber coming from an long-established system which was previously running another type of filtration (specifically, one that was not effective at keeping N and P from soaking into rocks/substrate) that one might get stellar growth at first (for a period of months or longer) or might get the high-nutrient growth which then turns over to green, but eventually with all other things being equal, the growth turns away from green to a low-nutrient type of growth. So this might be something to consider if you are in this situation, and your scrubber might need to be re-sized depending on the circumstances. This also might be one factor in longer term scrubber users finding that switching to a smaller feeding-based sized scrubber results in better growth.

Waxing on....

[Ace25]

Ya, everything you said... OR.. just dump a lot more food in the tank, everyone will be happier for it. (That's my philosophy anyway on the second part of your statement)

[SantaMonica]

Yes that's how it works. But then it's time for more feeding, the way it should have been from the start.