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General advice on 20gal system

Aqua noob

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I have a 80L (20gal) system, 40L sump, 40L display. It is nothing like the splendid systems I see on this forum. At all, but it’s what I got. 




Was out of work when I decided to start the marine (the irony) so it’s like diy


5 months running incl cycle. Livestock in order snails x 15 , Zoanthids, Xenia and sweeper frags, candy cane frag, branching hammer frag, bubble, plate, clowns x 2, cleaner shrimp


Return pump +/- 140gph, skimmer is 420gph pump into diy housing, fuge is chaeto, the fuge divides are mirror glass facing in (keep light) growing chaeto with a 20w LED flood, wavemakers 110 sun sun cheapies, rated 500gph each, one keeps floor clean other angles to the surface. Diy RGB LEDs about 28wats worth




General conditions of water: 


Nitrates to date are generally undetectable

Phosphates 0.01 

Ca 450-470 tested weekly 

mg 1350-1400 tested weekly 

Alk 10dKH tested weekly 

ph 8.2 - 8.5 tested weekly 


Dosing 2g ABC+ per day 

I make Alk adjustments with seachem reef builder to replacement water or tank where necessary 

Top up about half a gallon RODI per day 


Feed once a day marine s pellets soaked in Rodi 

Feed shrimp weekly in bigger pieces to bubble/plate etc 


i siphon excess food/waste off the floor and rocks weekly. 


I change 15% water weekly 



Candy cane and branching hammer will not perk up, the look glum as hell. Surviving, but glum, have had them for at least a month. They are both in medium flow areas, not direct




Zoas,clowns, snails, Xenia, bubble and plate look ok. 





Existing problems are: 

Stray voltage (I ended up making a grounding probe for the tank)

Lights, I know now that they don’t cut it in general


My questions are:


Is my tank turnover too slow/fast?

Is having chaeto + skimmer too much filtration?

Is my flow + 2x wavemakers too much flow for the small display? 

How sensitive are the cane/hammer to light/flow, if light and flow are not the problem, then is the problem perhaps a nutrient or placement issue? 

Is having undetectable nitrate and low phosphates a good thing are is there a target value I’m looking for? 


I do realize my lights are probably not cutting it, I have a TC420 +3w led combo type light on the way. But would it be such an issue on such a small tank? 


That being said, I don’t want to leave it to chance that the problem with the coral is lighting and possible minor current in the water. I want to be SURE I have everything else in check while I wait for my new lights to arrive and while I save funds for new equipment, everything else being flow, filtration, nutrient values. 


Please assist where possible, all suggestions welcomed, please don’t tread lightly with commentary. 



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Pretty neat system there.


What is the total turnover rate? You can  add up all the gph and then divide by gallons in display.


For soft corals and lps you want 20-30 times turnover. Alot of them don't do well with heavy flow which usually causes them to retract and cause torn flesh.


I'm not familiar with the lighting but lighting is important for corals.


Low nutrients can be the culprit as well. You want nitrates between 2-5

It may be too much with the skimmer and chaeto.


Do you feed your corals?



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Hello Clown79


thank you for the reply


Display tank 10gal sump 10gal

Pump is 140gph

thus turnover is 140gph / 10gal = 14 x ph ?


Perhaps a a bit lean you think? I can double it over the next week by opening the valve more each day and check the result. 


For a lighting person that may read: 


RGB is just 5050 leds in a strip, red green blue, with fixed spectrum, blue somewhat falls in the photosynthesis region the red is slightly. 120 LEDs @ 0.3w each. Im running all blue, 21 green, 42 red. 



Feeding corals yes, but only pellets the fish don’t eat being Hikari marine S. And once a week with normal frozen shrimp cut to sizes to suit each coral piece. 



I figure i need to get a test kit to check nitrate / phosphate more often so I can test the too much filtration theory. Thank you for that comment. At the moment i test once or twice a month at lfs. I have only got Red Sea Ca mg KH and Ph test kits with me. 

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So you only have the one powerhead for flow? If so 140gph would be low.


You have flow from the return pump from the sump as well.


As for the lighting. What's the spectrum?

For corals 10,000k to 20k is the optimal spectrums. 

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Sorry to correct, 140gph from sump + 2 x power heads at 500gph each.


So flow going through the tank (in and then out) is 140gph /10gal = 14x per hour. Power heads generating flow within the display itself amounts to 1000gph. 


In order of most useful to coral photosynthesis to least.

blue 465 - 470nm 

Red 620-625nm 

Green 520-525nm 


no whites at 10-20k ranges. I put a strip of white LEDs directly above the hammer and cane, it seems they have reacted to it, opening up a bit more.


I assume in short the problem would be “proper” lighting then.. 

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1000gph in 20g is 50 times turnover which is appropriate for sps but for Lps or softies it's too much.


What light fixture do you have? If it's for freshwater, it's not enough.


It's not just about the spectrum the lights are in but par depth as well.



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