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Holding Tank


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As people are probably aware of by now, if it's not simple, I don't do it - in regards to my fish keeping :)

I'm happy enough to put in an effort to begin with to make things easy later on - big believer in doing things right the first time.

So, I'm not particularly keen on keeping jarred out individuals in separate beanie boxes or take-away containers etc. I went out and got one of those little three bay things that has no sump or anything, and doesn't share water (holds a touch over 2L in each compartment) and heated it from underneath with a reptile heating cord. But I'm over having to do the water changes and cleaning every day (and I'm not impressed with the temp fluctuations with the cord) - bottom line - I wanted something bigger, something kept at an even temp, and something easier to clean and do water changes on, and for said water changes to be less often.

So, I'm going to build a holding system. This will be self contained in a single 2 and a half foot tank. It must be able to hold around 18 individuals in their own container, while carding them from others, and be able to share water so I only have to have one filter and one heater.

And I started this thread to give me impetuous to actually get it finished in a reasonable time (cant hide when everyone knows (oh, how's your fish room coming Razzi? ;) )

This is what I started with:

1 x 2'6" tank

1 x sheet of black corflute

18 x 1.25L soda bottles

1 x sponge filter

1 x heater

This stuff was gathered over the last year and was currently sitting around doing nothing - so cost has been negligible. I'm losing out on the $1.80 I could get from returning the bottles...but I think I can live with that.


1 x scissors

1 x knife

1 x ruler

I began by cutting the corflute to size so it fit down the length of the tank and the cross pieces to fit snuggly across the tank.


The idea here is to have each bottle sit in its own little compartment. I've still got three bottles to put into the above shown configuration. I can fit more than 18 bottles into the tank, but wanted to leave room for the filter and heater.

I'm still toying with the creation of the bottles/containers. Those above have been cut a little below the level of the surrounding corflute, and have holes in the bottom to allow water transfer, but I'm thinking I may change this to bottles with only holes in the sides. It will mean I need to siphon out the crap a little more often, but transferring the fish in and out would be easier (and I'm all about things being easier). Remember, this is a temporary holding tank only for the fish I'm moving on to new owners. My breeding stock is held in different barrack systems.

Now my offsider didn't have much input into the design, or the actual putting together of the thing, but his presence was still appreciated...


Once I've decided on the bottles configuration, I'll move on....stay tuned

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This is not my idea, originally, but one I've altered from other posts I've seen here and elsewhere (cant actually remember the thread I saw it on here - sorry, memory like a sieve).

The one's I've seen before allowed for the fish to see each other, I wanted them isolated, but still able to share water, and take advantage of the bigger volume of water to help keep parameters stable.

I've come to the conclusion that cutting the bottles a little bigger, (so they hold a litre if free standing - around 18cm on a 1.5L bottle), and then drill a ring of holes around the bottle 8cm up from the base, and then another ring of holes a bit further up, but below the water line, allows the transference of water in and out, but when I want to lift the bottle/container out (for sending fish or photographs), I can slowly lift the bottle up and allow the water to drain out of the holes, leaving the fish, and 500ml of water remaining in the bottle (no nets required). It means I'll have to siphon out each bottle, but that's a small effort compared to trying to get the fish out of the containers with a net or by hand (not that my hand fits all that well inside a 1.5L bottle anyway).

So, now I have to come up with another 15 bottles to configure in my newly decided upon way - more creaming soda for me.

At 18cm, I fill the whole tank to within 2-3cm of the cut bottle tops - this comes to 30L as an overall volume of the tank to hold 18 fish.


A closer look at my guinea pig...a young expendable (cull candidate) F1 Black Orchid CTPK (she was separated early due to fin melt but she's recovered quite well - just cant put her back with her siblings now or chaos would ensue...)


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I need to find a little pump to circulate the water better. The water temp has a 4 degree difference from one end to the other - all within acceptable limits but I'd prefer it was the same - so a little pump should work better.

Water changes: I siphon out the waste a couple of times each week, and do the water changes at the same time. At the moment, there are a couple of juvies still growing who are housed on the bottles so the water changes need to be regular. Once I've only got mature fish in there, water changes should be a little less often, and only require me siphoning out waste...but as this is to be my holding tank for fish preparing to go out the door, then they shouldn't be in there for long anyway :)

I have cut and cleaned eight more bottles yesterday. I shall drill the holes this weekend, so they should be in the tank Saturday arvo, and have fish in them not long after that, increasing the current tank population from 3 to 11 :)

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Hmm - played around with my holding tank last night - and found transporting the fish extremely easy...but transferring them from a holding bottle into another container - will take a second container to act as sleeve. I'm thinking a 2L bottle. If I slip the drilled 1.5L into the 2L, and then pour the water and fish onto another container, then it wont be so messy.

Feeding is another issue I need to think about. At the moment, only the front and some of the middle is populated, so I only have to take off one lid - I allow most of the condensated liquid to run off into the space occupied by the filter and the heater, and then rest it on a towel specifically placed for the purpose - no mess. But the light fixture rests on the other lid, so when I come to fill the back row, I'm going to have to find either a better light, or hang it, but the tank isn't on a stand, just some crates, and an mdf shelf (cant be on a shelf and still allow me easy access to all containers). Might get a free standing LED lamp to position over it instead...

In an effort to get more water flow, I've swapped the big sponge filter for smaller one - and then turned the bubble rate up to get much more agitation. I'll let you know how that works out - still may need a small pump.

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  • 3 weeks later...

Ok - so the holding tank is now operational and kind of passed it's first test.

I started jarring two spawns (CTPK # 2 &3 in my signature) and so new fish were going in fairly regular. I got to a population of 15 in the holding tank before I started sending them out the door to new homes.

The insertion of a sleeve into the holding bottle works well most of the time, but two found their way onto the wrong side of it and caused me momentary panic - but no harm was done - still might have to figure out a better way.

The 2L bottle as the holding container for the holding bottle (really should spend some time on a better naming convention) works really well. I cut a pane out of one side so the holding bottle is easy to slip in and out. The remaining sides of the holding container is slightly longer than the holding bottle so water runs out evenly from both. It has the added bonus of the indentations in the bottom matching the holding bottles so they kind of lock into place - the holding bottle cant roll around so easily.

I've raised the water level a bit more and changed the sponge filter for a smaller model. The smaller model sits around an inch or two under the water surface and I can turn the bubble rate up higher resulting in better agitation of the water allowing for a more even spread of the temperature -this is working well so I don't need a little pump :)

All the fish from the two F1 spawns have just about gone. There's only five fish currently left in the holding tank, and a couple of those will go shortly. The remainder are being kept for breeding and so will go into my breeding barracks until they enter the spawn tanks - leaving the holding tank temporarily empty. There is four fish left in the grow out from one spawn, and another F1 spawn isn't far away from starting to jar - by the time these are sorted and have had new homes found - then my F2 spawn should be ready for jarring...

Of course, other spawns are in the planning phase as well :)

Should be a good addition to the Fishroom this holding tank :)

Edited by Brenton
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