gws3

Oh, and for anthias, I would suggest a few of different species than a few of the same species. This has worked out better in my experience. Too much aggression in the smaller tanks with multiples of the same species.

I can give some relevant experience from my Red Sea 425XL. It's pretty close to a standard 90 gallon in size, but 22" wide instead of 18". I recently moved a purple tang out of it as it had gotten too big and boisterous for that size tank and a few of the other fish would hide a lot due to his energy. The remaining largest fish is a female watanabei. I think it was really a male with female markings, but that's another topic. I deiced to get a smaller female watanabei and see if they would make a pair and if the female would transition to a male. This worked out beautifully and the female turned into a male within a few weeks. He spends a lot of the evening doing his mating dance to impress her and chases her around the tank. This is fun to watch. However, he's become a lot more aggressive as a result. He used to be very slow swimming and laid back. Now, the other fish have learned to keep out of his way, and he is now the boss of the tank and acts like a dominant male. It's borderline too small of a tank for the pair of them, but currently it's working out ok. I would definitely not try to keep a mandarin and or pipefish in there with them. Those fish are too slow moving and delicate, they would be very stressed by the behavior of the mated pair. I wouldn't recommend keeping those fish in a 90 regardless unless you have a prolific amount of pods. I don't think their dietary needs would be met. In fact, I've tried both of those in that tank over the years and they do not last long term even though I was supplementing their diet with a constant supply of baby brine shrimp. The tank needs to be very rich in microfauna to be a good environment for them in my opinion. I do have a bimaculatus and sunburst anthias in that tank. They are doing fine, but you want to be feeding a few times a day. For tangs I would consider a yellow or tomini. Stay away from the tangs that grow larger and/or more aggressive. You can keep juveniles of larger tangs, but need an upgrade plan for when they get closer to maturity. Other good fish to consider are chromis, more peaceful damsels, royal gramma, flasher and fairy wrasses, dwarf angelfish.

Playing devil's advocate here... but if the UV was effectively killing bacteria in the water column then how could bacterial pathogens be spreading from coral to coral? I completely see your logic though. I've been reading and watching more videos about the microbiome lately, and it's so complex it generates way more questions than answers for me. I know Eli (Aquabiomics) has observed a strong correlation between people that run UV and greatly reduced pelagibacteraceae populations. That would indicate to me UV is more effective at killing certain bacteria populations than others. I believe the population is based on the water column sample only, and the swab is used for pathogens. I could be wrong here. You could also swab the effected corals. I think there's a reefbuilders article by Paletta where he did this to determine what bacteria was acting as a pathogen on his sps with necrosis. That article is a good read as it discusses how different bacteria require different strength antibiotics.

@nburg Did you already treat with OA? If not, I think it would be good to do aquabiomics before and after. It may identify a coral pathogen in abundance. It will also give you a before and after picture of the microbiome to know if the OA has the narrow scope of impact that you anticipate. You could also consider much stronger OA or Cipro baths for individual corals.

Having a healthy population of nitrifying bacteria is a good thing I'd say. How does the tank and corals look? What is your PO4 level. I wouldn't worry about it if everything looks happy.

Keep in mind NO3 is at the end of the nitrogen cycle. Zero NO3 does not necessarily mean you don't have any nitrogen available to organisms via ammonia or nitrite. If you're feeding the tank there is nitrogen being provided and consumed. It's likely bacteria consuming it. Keep in mind they need nitrogen, phosphorous and carbon. 0 nitrate could mean nitrogen is the limiting resource. I'm a proponent of controlling nutrient import and export in more natural ways before resorting to using chemicals. To increase your nitrate adding fish and increasing feeding is the way to go in my opinion. This is the approach I take first. I suppose I'm being a bit hypocritical though, as I use LaCl to keep phosphate in check. My PO4 levels will increase without it if I'm trying to maintain NO3 levels via nutrient import. Another interesting consideration I've heard is NO3 is in the water column and doesn't bind to organic surfaces like live rock, while PO4 does. So PO4 has a sink in a sense, if PO4 in the water column drops it will be buffered via PO4 bound to the live rock. If NO3 in the water column is consumed it would need replaced via import.

Talking to Tony, he is looking for people to come rescue fish/corals/rock tomorrow morning. It sounds like the tank is without power, but fish were still alive today. Please post here if you're planning / able to rescue livestock tomorrow. I may be able to get out there tomorrow to help with the fish if we don't find someone else. He said there are about 15 fish.

I wouldn't worry about the elevated lithium levels, it's from the salt mix. I've been using Instant Ocean for many years, it's always in the 300's, and I keep tanks packed with SPS.

probably milka stylo

Do you have a mesh lid? If not, you'll want to get one first. Wrasses will eventually jump out if not. I second that Melanurus are going to get too big for a 40. They're very active swimmers too. I had a big one in a 8' x 4' tank and he patrolled the whole thing every few seconds. Leopards I don't have experience with, but I believe they need a deep sand bed for long term success. Six line are hit or miss with aggression. I like the recommendation of Lubbocks for a 40. That's a pretty, small and peaceful fish. Any smaller Cirrhilabrus species would likely be a good choice for you.

Cyanobacteria. Siphon it out the best you can. Then use a powerhead to blow off the detritus on the rock. Bump up flow in that area slightly. See if it comes back before doing anything else. Patches like this are often caused by an area where detritus has settled and the flow is weak.

Chemiclean is an antibiotic. There are plenty of folks who have used it without issues, but something that indiscriminately kills both good and bad bacteria could have harmful effects. It may kill the cyano, but it's unklikely that it will fix the underlying issue that's allowing cyano to fluorish. What the OP has is not a deep sand bed. It's a shallow bed of very coarse material. The do not function the same way. I agree with you deep sand beds don't seem very common anymore. It's better to do a number of small water changes vs one large one. I wouldn't go over 50%. More importantly make sure your new water is similar ph, salinity, temp and alkalinity. Also that it's well mixed. 24 hrs with a strong powerhead should be fine. I'd be more worried about a sudden change to one of those parameters than boosting Ca or Mg quickly.

I think you've done a good job getting your nutrients at a better level. Keep up with the WC's and the phosphates should keep coming down. Definitely change your salt. No decent salt should be mixing up with Ca and Mg so low. You definitely want to get those up. Ca in the 420-450 range. Mg I like to run elevated at 1400-1500, I strongly believe this will help prevent some of the algae growth. IO or RC would both be a big improvement over you current salt if your test results are correct. How attached are you to your shallow "sand" bed? When I look at your tank pics the impression I get is you have a low flow area at the bottom where detritus is collecting. This is likely be fueling your algae and cyano growth. Personally I would remove the sand bed. This will allow detritus to collect in certain areas on the bottom glass where you can siphon it out regularly. Do you have a pressure washer? I'd be removing a piece of live rock every few days and pressure washing it to combat the algae. Just one piece at a time so bacteria can re-establish. Longer term, if the tank is too small to add an aggressive herbivore/grazer like a tang, you're going to need more clean up crew to keep the rock clean IMO. I'd add something like 30 astrea snails and 50 mexican hermits. Reeftopia or Salty Bottom Reef are good sources. One or two snails aren't going to move the needle with how much algae you have. I liked Nikki's post #21. I would take this tank back to absolute basics. You could probably run this tank's chemistry successfully with just water changes. Add some clean up crew and keep removing algae/cyano manually. You could treat the cyano chemically, but this is a band-aid fix IMO. I think you've got a big nutrient sink at the bottom of the tank and not enough clean up crew. You flow is probably on the low side based on the type of corals you're keeping, so there's not enough flow to keep the detritus suspended in the water column and get it to your sock & skimmer. This is where running bare bottom would really help out.

Look at the Hanna HI98319, it'll give you the tenth of a ppt you're looking for. Mine consistently reads 0.8-1.1 lower than the TM hydrometer, but it's consistent. What you could do ii check the HI98319 against the hydrometer every month or two, but use the HI98319 regularly. It can be used in tank, so it doesn't require any saltwater to be removed.

Oh, and for temp probe calibration I use another old school device... a mercury filled glass thermometer. Forget the brand, but it meets ASTM 17F. Never requires calibration and it'll never change. Just have to handle it carefully. Also, they're difficult to acquire as they can't be shipped to Maryland due to the Mercury. Not sure if the same rules apply in Virginia.