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soft corals died and replaced by green algae


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My 29 gal nanocube reef-only tank ran fine for the first 6 months. It housed lots of very large mushrooms, zenias, star polyps, and zoanthids. I added some leather corals toward the last. During month 7 and 8 the mushrooms slowing disappeared and the zenias wilted. During month 9 the candy cane corals, bubble corals and zenias died. In their place lots of green hair algae grew. I was on vacation for 3 weeks and my tank tenders did not know what to do.

I have had the water tested at two stores and all is fine except that the PH is 7.9. Here is what I was advised:

1. add buffer.

2. add iodine. May be why soft corals died. (I tried more light, less light, more flow, cooler temps)

3. cut the main light to 4 hours, auxiliary light to 10 hours

4. hand brush off the algae and change the filter

5. do a 20% water change

6. wait a month

Rest of the story: temp ranges 79-81, one scooter bleeny fish, two feather duster worms, two sea cucumbers, two emerald crabs, 4 blue-legged hermit crabs, 1 cowrie, two snails that live in the sand, 5 trochus snails (or similar). Very diligent owner who is about to give up.

Am I doing the right things if I follow this advice?

And any suggestions for reading material on tank remedies? I just don't have answers when the tank changes. I try as much as I can think of.

Thanks for your help and support.

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Most of the advice sounds good. I think though it might be a good idea to find out why the ph is low. There could be a couple reasons. CO2 pooling. Meaning the CO2 sits on the surface of the water. This can be alleviated by more surface agitation which is a good thing for gas exchange anyway. Also a fan blowing across the surface will help and will also cool the water temp.

I am not sure I would add much iodine. I try not to add anything I can't test for. I would read the label and dose very carefully. Maybe do half what it calls for and see if you see good results.

Another thing that might be a partial culprit is your bulbs. If you are running PCs they have a tendency to shift spectrum around the 6-8 month mark. This can cause problems for your corals as well as encourage algae growth.

I would recommend doing a 5 gallon water change every 2 weeks while scrubbing the hair algae off. Actually it wouldn't hurt to do that on a continuous basis and could be very beneficial.

As for the lighting times. I have heard that algae takes longer to get ramped up than corals do. So if you could put an hour break in the cycle it keeps them from getting the full benefit of the light. So have your actinic on their normal schedule and then have the main light on for 3 hours, off an hour, and then on again for 3 hours. I have read of people having success with that.

My other thought is it seems like you are a little overstocked with inverts for your tank. I would look to get rid of at least one of the cucumbers and the cowrie. I am actually surprised they are finding enough to eat in a tank that size.


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I suspect the bulbs as well and don't add anything unless you test for it. Also, what species of Cowrie, some actually eat soft corals so be careful. Could also be chemical defense from leather. That is a lot of softies in a 29 gallon. If you have a lot of green algae, then the tests aren't showing something right.


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Many thanks for your comments. I, too, don't like to dose my tank. There have been times when it was beautiful without adding anything. As for the lights, well, that's been a problem. At 6 months I was prepared to change out both bulbs but the Chinese ship bringing the blue light bulbs did not come so no store had them. Instead, I was advised to buy a new day light and use the 6 month old day light as the substitute for the blue dawn dusk light (that actually burned out at 6 months). So I run the new day light for 4 hours (will split as you suggested) and run the old day light bulb for 10 hours.

I noticed this morning that there was no coraline algae growth on the glass as had been previously. I used to have to razor it off. My two sea cucumbers are both filter feeders, one on the side of the tank and one under the sand. I feed phytoplankton twice a week for them and the feather duster worms. The cowrie is a white shelled species commonly called a money cowrie. Has a black and white mantle.

I am surprised to see advice about 'too many softies'. When I bought the tank I was told I could pack it full of soft corals, just no hard corals. What gives?

I think the larger emerald crab has died. I haven't seen him for a month, but do see the smaller one ocassionally.

And I suspect the water is not being circulated enough. I have a fan I attach to the lid so will begin to run that one a regular basis.

Finally, if you or anyone you know would be willing to pay a house visit, I would willing to contribute toward their next fish. Thanks, Ann

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Hi Lee,

Thanks for your suggestions. Please see my reply above. Lights are a problem I suspect. Maybe that's why in the beginning everything was so healthy. Ann

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If Gabriel swings by you should be just fine. I leave for Vegas tomorrow and don't return to Thursday but would be happy to visit and help if Gabriel can't. When you say "Chinese" regarding lights I suspect you might be buying cheap bulbs. Don't. For all you spend on everything else, don't skimp there.

A lot of softies can be done in a tank, but sometimes the chemical warfare can cause problems. The Money Cowrie is GREAT and just fine for your tank.

The cucumber in the sand bed doesn't need any phyto, but the other one does. With a lot of softies good water movement and running carbon can help with chemical warfare.


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  • 2 weeks later...

+1 for all thats been previously said.

pc's have a fairly short life span and do shift spectrum after about the 6-8- month mark. unfortunatly they dont just crap out and stop working, but instead shift spectrum to one better suited for growing algae rather than anything else. :P i hand write the date with a sharpie right on the plastic base of the light bulb when i change it to a new one.

i would actually change water a little more ofeten than gabriel has sugested. 2 weeks would be about the longest you would want to go without a water change, and 5g sounds about right. one thing to remeber is that with more frequent water changes comes less frequent dosing. i do 2 water changes a week in my BC14, but they're small, about 1 to 1.5 gallons. this helps to replenish alot of the trace elements without me having to manually add them seperatly, although i do.... :)

i agree with not dosing things that cant be tested. alot of the additives on the market not only encourage coral growth, but algae growth as well. i add 5 drops of iodine per week, and do it very timidly. some times i just skip it. i dont like additives because of the ease of an accidental OD.

jam packing a small tank with TONS of softies in my opinion is fine, except for one thing, the aforementioned "chemical warefare"... activated carbon is a MUST with softies! all it takes is one coral death to start a dominoe affect of die off, chemical release due to die off, followed by more die off and the cycle continues... some corals tolerate it better than others.

the algae can be attributed to number of things. all of the previously mentioned topics will spark algae growth in nuisance perportions. all the rock scrubbing in the world won't help get rid of the algae unless the underline cause is addressed and remadied... ( did i spell that right??? remedy, blah!) over feeding, over dosing, lack of water changes, water changes with tap water, detritus accumulation, lack of nutrient exportation... the list for algae outbreaks goes on and on and on and on and on and on and on..... your tank in particular is easily modifyable to accept a protien skimmer and a fully functioning refugium.

what i would suggest, and what i always sugest, is doing things the full on HARD way! :lol: this means add the refugium, add the skimer, follow a more frequent and strict water change regiment, keep fresh light bulbs, keep and frequently replenish a bag of activated carbon, and periodcally test for the entire battery of water parameters.

this sounds like alot more work than it actually is. the bulk of the owrk is simply setting up the fuge and testing the water params. another thing i forgot to mention, but was already mentioned, is how much of a particular product your dosing. gabriel had the 100% right idea about strictly folowing the manufacturers recomendations for dosing, and then cutting thier recomendation in half. for all we know they may base thier dosing schedual on a fully stocked tank of 5+ year old matured colonies when our tanks may be full of brand new baby frags. obviously the larger colonies are going to use more of the product than our small frags are. in which case, if we followed thier recomendations to the T we would actually be dosing way too much. i guess the comparison woud dosing a tank with corals, and a tank without corals.

ill post a few pics of the mods ive made to my BC14. all of them very easy, and very cheap!

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what i did to add a refugium was scrape the black paint off the back of the tank, but only on the middle chamber. then i added some live rock rubble and cheatomorpha. i also added a clip on lamp and used a 10w spiral pc bulb to light it. this was an EXTREMELY EASY modification to make, it only cost me about $20.oo using stuff from walmart. and im absolutely positive that this application is the single most important system currently employed on my tank! at first i was nervous about having the lamps reflector pressed right up against the glass because of heat related issues, but as it turns out, its more beneficial than i had realized. i have only the stock lighting and no other means of heating or chilling. the heat from the stock lights keeps my tank plenty warm during the day. but when they turn off i have nothing contributing to heating the tank. now i have the refugium light that operates on a reverse photo period. so when the main display lights turn off, the refugium lights turn on. they light the refugium, keep the tank warm in the absence of the main lights and help maintain a stable ongoing PH. PH will lower in the presence of elivated co2 levels. when lights are off, photosynthesis stops, no o2 is being generated, and co2 has the opportunity to accumulate. this accumulation of c02 has the potential to lower your ph, which is undesirable.

those are the side benefits to this mod, the real benefit and the main reason for the mod is obviously the nutrient export capabilities of the system. all the dissolved organic compounds that build up in the tank dont have anywhere to go if it werent for water changes, protien skimmers, and/or refugiums. the macro algae used in the refugium will utilize these dissolved organics to grow, thereby reducing the total percentage of dissolved organics left in the water for the undesirable algaes to use.




i also use the BC nano skimmer. i would use something bigger and better but nothing else will fit! i use that in the fist chamber. you'll notice in this next picture that i have a pad of filter floss placed on a plate that sits over the refugium. this filter pad helps catch alot of the suspended detritus before it has a chance to settle in an area of the tank where i cant siphon it out. siphoning out detritus plays a huge role in water quality. as detritus has time to settle, it also has time to dissolve. if you can get to it before it starts to turn into a dissolved organic compound, the better off you'll be. thats why its easier to catch it as a somewhat solid matter. once it dissolves the only way to get rid of it is with the refugium, a protien skimmer, or water changes. i change the pad about once a week. the material is very cheap. i got mine from aquatek.


in those 29g all in one tanks there is normally enough room for a decent skimmer like the saphire skimmer, or the tunze nano. i would recomend it if you can.

as for carbon, i just have a mesh media bag with about .25 - .50 cup of carbon, and i set it in the area where the water from the second chamber enters the third chamber. i change out about half of that every 2 weeks. this is a neccesity if your going to keep alot of soft corals, and i cant stress that enough! the only way to get rid of the toxins secreted by soft corals is through water hcnages and the chemical absorption properties of activated carbon. if the toxins are allowed to accumulate, not only will it kill everything in the tank (thats what its meant for in nature) but it poses an extreme hazard to you as well. especially in the case of some zoanthids which emitt a very powerfull toxin called "palytoxin". its very noxious stuff that nobody should mess with!

if you'de like you can check out my thread on reef central. it shows the battle i fought with nuisance hair algae, flatworms, and a killer clown fish :lol: it really shows the affects that my tiny little refugium had on the whole system! it also shows that it is possible to cram soft corals into every concievable open space someone could possible glue a coral frag! :)


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