Hey, I had the same thing happen to my hang on fuge. Where my cheato turned white throughout the mass all at the same time. So would you suggest that it is too little light? I have around .25 nitrates, .3 phos and only an anemone with some fish in the tank at the moment. I have the tunze refugium light submerged. But it is a 10gal hang on fuge that I made, and the cheato is at the bottom so perhaps there is too much distance between the light and the cheato? I am thinking to buy the kessil H160 to increase the par output.
that def sounds like its a case of one or more of "too low nutrient/too low light/too low volume/too low competition". Lets go thru each:
On nutrient:
1) do you mean .3Po4 or .03 PH4? .3 is wayyyy too high and should have cause other issues with your tank (ie massive algae/diatom bloom). in either case - chaeto absorbs no3/po4 in a fixed ratio so it will be limited by the no3 in your water.
2) the .25 NO3 is definitely on the low side - but that is only what's in your water. However, you gotta think about why its so low - Is it because you just have a low bioload now? or is it because the No3/Po4 is already all absorbed by the algae growing in your DT? From what you mentioned - i suspect its the former since you said you only ahve a few fish and a nem. But if it's the latter, then you can also tell easily by how much algae is in your DT.
2) If it's due to low bioload, then really your system doesn't need a fuge yet. Just wait until you have more stuff in the DT before you activate a fuge
3) If there's a ton of algae growing on your DT, then its a competition issue (more on that later)
On volume:
1) How much chaeto did you start off with? in terms of the no3/po4 absorption rate - just because you have .25 NO3 doesn't mean that all that will be available for your chaeto to absorb. Since it's measured in PPM, we gotta think about how much "surface area per volume" is exposed to how much light between your fuge vs DT to see relatively how effective it is being absorbed everywhere. looking at your build thread, you ahve a 65G DT. How how much surface area in your DT compared to your fuge "per 10 gallon"? you don't have to be exact and can just approximate. Chances are your DT has much higher surface area per 10G b/c of the various rockwork etc where algae is growing and absorbing light.
2) So - even assuming SAME light intensity - the lower surface area means that less than the full .25No3 is available for your chaeto.
On lighting
1) i've actually heard good reviews on the Tunze submersibles, esp if you submerge it and put right next to the chaeto, though it probably isn't not as strong as your DT in terms of raw PAR output. having it much closer should narrow the gap a bit. looking at your built thread it looks like your fuge is "thin but wide" so maybe the light is not evenly distributed - ie the far end may be too dark. Keep in mind that light intensity decreases inversely by the square of the distance - meaning, 2x further away means 4x less light. 3x further away means 9x less light.
2) Getting the H160 may not solve your problem b/c it's a even more "concentrated" source of light instead of the Tunze light strip. B/c i believe your light "spread" problem is a bigger issue than light "intensity" problem.
3) if indeed you determined it's a light issue and not a volume/nutrient issue, then maybe just get 1 more tunze and put on the opposite side, or 3 (put one in the middle), depending on the exact dimensions and spread of your fuge.
On competition
1) if you have very strong algae growth in the DT, then it boils down to competition so I would recommend increasing the first three points. I would not recommend "maxing" one while ignoring the other b/c there's a maximum thresold to all of them. IE - if you don't have enough nutrient, or not enough volume. putting 50 tunze lights in there won't help b/c chaeto has a maximum light absorption threshold and will probably die from burn out. I also wouldn't try to stuff the fuge full of chaeto b/c if its another factor causing the issue, then all of those will melt and crash your tank.
2) manual removal of the DT algae to reduce the competition from DT,
3) reduce lighting on your DT (if ur livestock can tolerate it).
Taken everything together - my money is on the theory that you don't have enough bioload right now given the few fish + 1 nem in a huge 65G. So i would recommend just don't use a fuge b/c you have low nutrient and it'll be very difficult to bring that last .25 NO3 down to 0 (given what i discussed above with the volume, surface area, etc). But, you know your own tank better than I do, so.. adjust accordingly based on what you see
Good luck!
