Two tanks, one sump.

[duanes]

I don’t think hob overflows should be a problem as long as I don’t keep plants in the tanks. Nothing else could clog it.
Running the tanks top into bottom- into sump is an interesting idea. Seems a little finicky, but interesting.



Thank you for chiming in! Do you happen to remember what gph the pump was that you used?
I wonder if it would be possible to cut the existing stand in half, frame the bottom of both halves, and stick a sump in the middle between them.
(Tank 1) sump (tank 2)

You should have both tanks up, and the sump at the lowest point (as said above), this is what I meant about using gravity. Tanks don't all need to be exactly the same height they can be staggered, but higher than the sump.
I have used HOB overflows, but agree they can be problematic, especially if air bubbles get trapped in the U tubes, the chance of overflowing tanks onto the floor is almost assured.

I prefer drilled tanks, it is much easier than it sounds, and once I did it I wanted all my tanks drilled.
Pump per gallon flow can vary, per size of tanks, for 4 tanks I usually used 3600 GPH , 2 tanks minimum 1200 GPH, 1800 better.

Above an overflow box running from one tank, down to another, then to the sump.

in the tank above the overflow runs a line diest to the sump.

 

[duanes]

Thank you for chiming in! Do you happen to remember what gph the pump was that you used?

I should have mentioned this before
One deciding point, on the pump size, has a lot to do with the type fish kept.
I most kept rheophillic cichlids (Rheoheros, Chuco, Tomocichla) and riverine (Cribroheros, Vieja etc) species that like lots of flow, and highly oxygenated water, so I used higher flow type pumps (3600GPH range).
Some Lacustrine species or slow moving riverine, might prefer less (1200 to 1800GPH) .
Or with oxbow, and swamp fish, (discus, angels, some Anabantoids) a low flow pump would be apropos, so with two tanks (500 to 750GPH).

 

[MrsE88]

Oh, I see. I didn’t know air can get trapped in the u tubes. I thought clogging was the only concern.
Hmm... maybe I will have to drill if I want to have a sump. Ugh.

I should have mentioned this before
One deciding point, on the pump size, has a lot to do with the type fish kept.
I most kept rheophillic cichlids (Rheoheros, Chuco, Tomocichla) and riverine (Cribroheros, Vieja etc) species that like lots of flow, and highly oxygenated water, so I used higher flow type pumps (3600GPH range).
Some Lacustrine species or slow moving riverine, might prefer less (1200 to 1800GPH) .
Or with oxbow, and swamp fish, (discus, angels, some Anabantoids) a low flow pump would be apropos, so with two tanks (500 to 750GPH).

Well, koi will be kept in them for 5-6months. Just depends on how long winter lasts this year.
After that I’m not positive. I’d love a flowerhorn and perhaps I’ll give a tank to Oliver’s son or my female green terrors.

I really love the pump I’m using in my current sump set up, but it only has a flow rate of 1,320gph. The next size is 2,377. Do you suppose that would be better if I fill both tanks off it?

 

[duanes]

1320 should be plenty enough overwinter koi (depending on their size).
With my HOB overflows, I always kept a proper length airline tube, hanging near to each over flow box, if I noticed air bubbles starting, I'd restart the siphon, on that U-tube.
Drilled are so much less stress, and once you drill one, you'll wonder why you waited.
Large tanks are much easier to drill than small ones, I've drilled them with fish inside, I just drop the level to below where I want the hole to be.
A good diamond drill bit will handle maybe 10 to 12 tank holes.
I like the hole to be near the surface, on either a small panel, or the back.

I cut a template out of junk wood to help hold the drill steady, clamp it on the tank and slowly go for it, using plenty of cooling water on the bit for glass.

 

[MrsE88]

1320 should be plenty enough overwinter koi (depending on their size).
With my HOB overflows, I always kept a proper length airline tube, hanging near to each over flow box, if I noticed air bubbles starting, I'd restart the siphon, on that U-tube.
Drilled are so much less stress, and once you drill one, you'll wonder why you waited.
Large tanks are much easier to drill than small ones, I've drilled them with fish inside, I just drop the level to below where I want the hole to be.
A good diamond drill bit will handle maybe 10 to 12 tank holes.
I like the hole to be near the surface, on either a small panel, or the back.

I cut a template out of junk wood to help hold the drill steady, clamp it on the tank and slowly go for it, using plenty of cooling water on the bit for glass.

I like the idea of using the wood. I don’t suppose you have a picture of the bit you use for drilling do you?
I have diamond tipped bits for a drill and dremel, but not the kind that make round holes. And the hole cutting bits I have I believe are only for wood.

I’m not sure what size the koi will be when they come inside, but right now the biggest two are around 12-13” I think. The smaller ones being over 6”. I have eight all together, so four in each tank to spread them out a bit. My two fancy goldfish will need to be in a different tank so they don’t get hurt by the koi. And I haven’t decided where the countless giant danios will go yet. They have been breeding in the pond so I have no idea how many I’ll have. Yikes!

 

[duanes]

Sorry no shots of the drill bit, I got it from a company called Jehmco, and because I wanted to use 1.5" overflow PVC, I asked for the bit that worked with it, they have a chart, for it, and a proper sized bulkhead. So from then on, all tanks use 1.5 PVC, which is harder to clog than any small PVC.

I used to over winter golds, and low together, and even some cichlids, in a kiddy pool,

 

[MrsE88]

Sorry no shots of the drill bit, I got it from a company called Jehmco, and because I wanted to use 1.5" overflow PVC, I asked for the bit that worked with it, they have a chart, for it, and a proper sized bulkhead. So from then on, all tanks use 1.5 PVC, which is harder to clog than any small PVC.

I used to over winter golds, and low together, and even some cichlids, in a kiddy pool,

Thanks I’ll look them up and see what I can find.
I’ve wintered my goldies and koi in the past, but I’m afraid in a tank that’s only 18” wide that if the koi spook they will damage the fancy goldfish’s swim bladders.
If they were just commons I’d house them together.