Plenum problem??

[sacramentofish]

I have a 1 inch plenum (dead water space) under about 3 inches crushed coral in a 38 G reef tank with minimal bio load. the LFS guy told me the plenum is a ticking time bomb and I should remove it. What do you think? Is the Plenum good or bad?

My chems are perfect except NH3/NH4 about .25 - I suspect this is due to my skimping on the LR and BR only about 40 lbs total, and only seeded with rubble about 4 months ago. There are tones of cops and bristle in the bed but the coraline is just starting to spread on the BR.

I am adding a 20G sump/fuge and add about 40 Lbs LR that should take care of the NH problem.

 

[reefrunner69]

What do you think? Is the Plenum good or bad?

I am not fond of deep substrate filtration, simply because there is an end product and the substrate acts as a sink for these products. The notion of whether a deep substrate is a timb bomb has been hotly debated, here and elsewhere for about a year. Some swerar by it and some swear at it, I personally have a DSB in a removable refuge and when I revamp my system will probably remove it all together. As for a plenum...I think you get the same benefits from a DSB without as much headache.

 

[sacramentofish]

what if I keept a power head running on an uplift tube connected to the plenum- basicly making it an under gravel filter?

 

[reefrunner69]

Then it would be an undergravel filter with all the problems associated with such.

 

[sacramentofish]

so.. shoulde I take down my tank and remove it or just leave it?

 

[bizzybeas]

How is your plenum constructed?

 

[Brisc0]

I have a basic pelnum myself, before i dropped in 100lbs of substrate I just tossed an undersized undergravel. If you have done something similar then its not as big a deal as making yourself a 3/4 inch gap all the way around the bottom with an "egg crate" sytle plenum which I consider to be a lot more advanced and require a much greater level of skill. The simple undergravel like I used right on the glass isn't going to give you as much surface area at the bottom to truely build up massive levels of anarobs.

 

[Bearfan]

***The title of this topic has been altered to reflect proper spelling by Bearfan***

 

[fishfreek]

***The title of this topic has been altered to reflect proper spelling by Bearfan***

8O

Must be a slow night at the Bearfan house. Guess the Bears arnt in the playoffs :|

 

[Bearfan]

Only on Playstation.

 

[Brisc0]

LoL you'll get em next year eh der bear fan?

 

[sacramentofish]

well I have a pvc/egg crate plenum/ screen with 3/4 inch dead water space covering the entire bottom of my 40 G tank. on top is about 60lbs of crushed coral.

back to my orginal question, should I remove it or not?

 

[smooth_rivers]

ouchie Bearfan, lol

 

[reefrunner69]

. on top is about 60lbs of crushed coral

Yes remove it, from what I understand about plenums crushed coral is too large a substrate for proper operation.

 

[bizzybeas]

I have real fine sand on top of my plenum. This is a tough topic, because everyone will have a different opinion. I am sure that someone probably has seen some problems with one, but I have seen some function for years and years with good results. 8O

 

[sacramentofish]

I have small 1-2mm crushed coral directly on the plenum screen about 1 1/2 inch deep, then another inch or so of 2-3 mm crushed coral on top of that. I have 0 nitrates/nitrites after 4 mnths. I think I will leave it in..way too much hassle to remove it and I may just do more harm than good.. on to my 30 g sump/fuge project..
thanks for the info. btw- just ordered 30lbs or hirocks.. just what I was looking for

 

[toddwess]

I have real fine sand on top of my plenum. This is a tough topic, because everyone will have a different opinion. I am sure that someone probably has seen some problems with one, but I have seen some function for years and years with good results. 8O

bizzybeas - I am getting ready to build my first plenum and would like to know what sand you used to put on top of yours. You say it is a real fine sand - do you know what the sand was? Was it southdown sand?

Thanks for your help, and any advice or wisdom you can impart on how to keep a successful plenum would be greatly appreciated.

Todd

 

[HoopsGuru]

I have 0 nitrates/nitrites after 4 mnths. I think I will leave it in..way too much hassle to remove it and I may just do more harm than good

Having 0 nitrates after only 4 months is not that uncommon, and IMO not a good indicator to the efficiency of the setup. Crushed coral is not recommended for plenums or any other deep substrate filtration. It will allow too much oxygenated water into the bottom layer of your estimated 2.5" of CC. Thus, I doubt you will get the benefits of having an anaerobic zone.

Crushed coral also traps a TON of detritus and should be vacuumed regularly. This will disrupt any functionality of your plenum anyway, or if you don't vacuum will just build up with detritus. IMO, you will be doing far more harm than good in the long run by keeping it in. I would either build a proper plenum or remove it and just have the substrate.

 

[sacramentofish]

What about all the disruption to the current sand bed comunity? I have TON's of bristles, britle stars, cops and mysis shrimps.. will the removal and addition of more sand kill them off?

I am expecting 30lbs of hirocks and have a 30g sump/fuge I am setting up, so I might consider pulling the plenum and moving some of the existing LR around to make room for the new base rock. I just don't want to chash my sand bed comunity by ripping out the plenum..

 

[HoopsGuru]

The CC should be completely aerobic at this point, I don't think it would cause an issue to remove the plenum plate and just have the CC (I would give it a good vacuum first to avoid a nasty storm of debris). If you would be considering removing and replacing the whole substrate then obviously you would lose most of the critters.