cleaning you`re tank

They will typically fall out of the siphon hose unless the hose you use is huge. You want a steady low flow in your siphon hose and not a gushing 1000 GPH pull.

The question of whether or not to siphon your substrate is going to depend on the type of substrate you used, the depth and your intended substrate usage. That is, if you have a Deep sand bed then no don't ever touch your sand bed. ever. If you have a standard level bed then have at it.

Cyno is part of a tank start up, and running process so the questions is what are your parameters?

Lighting type and length of time.
Chemical readings
Feeding schedule and amount.
Cleaning routine (which you gave)
Do you have a sump with filtersocks, or sponges to catch bubbles or detritus?
Do you skim?

How old is the tank?
Has it cycled (not I think so, the answer here should be at day X I got an ammonia spike at day Y i started to see an ammonia drop and on day Z I started to see a spike in nitrites and nitrates followed, you ideally should keep a detailed log of your tanks life. At the very least you should do this while new to the hobby)

Always remember that we are not in the because we keep fish and corals... We are in the hobby because we maintain water.

 

As a reminder, a sump that stays lit 24/7 produces no benefits. The idea of running macro in the sump is to absorb nittrates and phosphates, yes, however the idea is a reverse photo period to make up for the micro algae that grows during the day. by not running a reverse photo period you are forfieting one of the major benefits of the system. Also the 24/7 operation of the sump light is causing your issue. Reduce it to a 6 hour burst in a revers photo period to the DT.


Tank stock: Your mandarin is going to have trouble surviving long term with that many hermit crabs as competition. As a comparison, I have a 75 with three hermit crabs, tank stays clean. Mandarin is fat. More than a handful of hermits are detrimental, they end up picking the rocks clean, and then once they do they feed on inverts like snails.

Sump looks good, stay on top of the sock ( i know when it time to change mine because I miss it by three days and the tank ends up looking like crap lol) Otherwise you may want to up your skimmer a touch, I skim about two gallons a week from the 75 and about a gallon from the 40 in the same time. Sludge should be light to medium green rather than super dark and thick ( though once it builds up on the neck it will be thick)

8 months is still within the cyno window. But feeding and water changes look good. I still say light period is grossly too high and should be kicked down. I would cut it down to 4 hours a night for two weeks then bring her back up to 6-8 Probably 6 first and watch to see if PH stays nice and tight.

I have no experience with fiji mud, but what I gather its rich in minerals and densly packed. So nothing out of the ordinary, I would keep the set up you have, and maybe add an inch or two to the DSB. and remember to never touch it. ever. Otherwise I think you should be fine.

 

The sandbed in your tank can be syphoned. If the sand goes into the tube, you can just restrict the tubing to let the sand fall back out. Or, you can take a small section of the sand and aggitate it so the detritus becomes waterbourne and syphon that way. As stated, do not disturb the deep sandbed. If you want to remove it, do so slowly (sections of it) as toxins are in there. I would not suggest using the Miracle Mud as I don't think there is benefits...my opinion only... from what I thoroughly researched...no experience using it. The NO3 and PO4 are getting high, especially the PO4! The cyano in the sump is probably being caused by low flow/water movement, nutrients and the lighting. I've seen plenty of fuges that have chaeto with cyano on it...no cause for concern. Better there than in the tank. FWIW, I run my fuge light (LED) 24/7 and get excellent growth/nutrient export from the chaeto.