CUC Only Tank?

[ToastyFins]

Hi there! I’m a teacher trying to start saltwater aquariums in my class with my students. I wanted to keep it simple with FOWLR set-ups that are basically just one fish of their choice, a CUC, and some macroalgae probably in Fluval EVO 13.5 gallon tanks. I’ve had a 30 gallon reef tank for 16 years, so I know some stuff, but I’ve not tried smaller tanks nor so many at once (8 tanks, one per group). Also I have the added “fun” of navigating summers. I want to avoid what some schools do where they break down the tanks completely each year and re-cycle them in the fall (if possible). Here are my questions…
How often would you do water changes on tanks like these if it was you?
Would you recommend I got an additional, larger tank for the classroom for any logistical reason?
If I left the tanks running without fish over summer (like returned the fish but kept the CUC and macroalgae), what would summer care look like? How long can just the CUC go without regular feeding? I’ve never tried a CUC only tank, and I cannot see anything about it online.

Thanks in advance!

 

[threebuoys]

The need for water changes over the summer will be predicated by the cleanliness of the water during that period. You will probably need to add a few food pellets occasionally during the period, either manually or by an auto feeder. Not too much, but driven by the number of invertebrates, or you will foul the water. Keep filtration running and develop a plan for water evaporation. ATOs would be expensive for what I think you are looking for. Glass tops covering 75 - 80 % of the open area would slow evaporation a bit. Perhaps transition to fishless a couple of months before the school year ends just to be sure everything is working like you need. Also, no lights and not near windows or algae will likely create a big mess.

 

[ToastyFins]

The need for water changes over the summer will be predicated by the cleanliness of the water during that period. You will probably need to add a few food pellets occasionally during the period, either manually or by an auto feeder. Not too much, but driven by the number of invertebrates, or you will foul the water. Keep filtration running and develop a plan for water evaporation. ATOs would be expensive for what I think you are looking for. Glass tops covering 75 - 80 % of the open area would slow evaporation a bit. Perhaps transition to fishless a couple of months before the school year ends just to be sure everything is working like you need. Also, no lights and not near windows or algae will likely create a big mess.

That makes sense. Perhaps an extra larger tank might be good then? I can use it as QT during the year but also put all of the CUC in it over the summer w/ ATO and an auto-feeder and just keep the other ones running with live rock/sand only and lights off? Not sure how long a tank can go without anything in it (I'm assuming months evaporation aside).

 

[threebuoys]

That makes sense. Perhaps an extra larger tank might be good then? I can use it as QT during the year but also put all of the CUC in it over the summer w/ ATO and an auto-feeder and just keep the other ones running with live rock/sand only and lights off? Not sure how long a tank can go without anything in it (I'm assuming months evaporation aside).

Probably will be fine with this approach. You will need to be careful when you move life back into the smaller tanks that ammonia doesn't build up. You will have to top off water then too.

 

[jda]

You just need to feed the CUC. Pellets work fine for crabs and shrimp. The snails can eat algae. Auto feeder with pellets can last a long time.