What’s a must-have fish for a peaceful 75 gallon community?

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Apr 5, 2023
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Really just asking: I’m trying to figure out if I can get any new cute behaviors or pretty colors in. It’s a peaceful 75 gallon community, planned to have mostly tetras, some fin-nipping, albino Cory catfish, and a dwarf gourami (I have a reputable seller). It’s also going to be very soft, acidic water, as I’ll be using a RODI system, cut with some tap for minerals. I’ll be aiming for a ph of 6.5 and a hardness of 10 DH. Very slow water, no predators beyond a BN pleco that might eat really small shrimp or snails. Any must-haves that would fit?

Edit: also, can I have Pygmy Cories in this tank, or is it too big for them?
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I think you could put pygmy cories in there, and a lot of them too

This may be controversial, but I had a 55 that had both a dwarf gourami (one I knew to be passive) and a breeding pair of triple red cockatoo apistos. The pair was active constantly, never got too agressive, and demonstrated some really really cool behaviors. The tank was very heavily planted so lots of babies ended up living, despite the dwarf gourami and shoal of harlequin rasboras. I couldn't recommend the set up more. The female constantly cleaning out their cave and the male's dedicated defense--it's beautiful to watch. Some people would say it's too risky because of how aggressive either can be, but with a tank that size and planted I think it could end up great. Or even worth replacing the gourami. Keep us posted!
I agree with Ellie that it is controversial to mix cichlids and gourami.

I don't recommend a pair of apistogramma here due to the corydoras. Corys bimble around with no awareness of territory. Apistogrammas who are breeding will attack the cories.

If you're choosing fin-nipping tetras you are really limiting the choices for tank mates. Gourami will be unsuitable .

I don't mix regular and pygmy cories to ensure the pygmies are not out-competed for food.

What is the reasoning for 'very slow water'? Again, this really limits options.
"must have" is in the eye of the beholder. What I must have and what you would are radically different in most cases, and what I would have thought I needed in there ten years ago compared to now is not even close. There are too many factors, with local availability being key.

What is must have is a vision of why each species you choose fits in the idea of your tank. No impulse or convenience buying - but a clear idea of what you want to find when you look into your tank. If that search leads to you encountering species that weren't in your plan, be sure to google 3 or 4 reputable sites (Seriously Fish is a good start) before you jump.

Remember slow moving is generally lower oxygen level, so fewer fish.
I’m adding a air stone, as I also plan to run co2 in this tank. Probably kicking out the gourami and replacing him with a all-female group of Bolivian rams to stay with the South American theme.

The slow water is for a few species of tetras I want to keep that aren’t big enough to withstand strong current (aka, ember tetras), so I’m just using a canister filter to get slow flow.

Most of the “must-have” fish here are just the fish my dad likes and really wants me to have, so they’re on here because of that. I’m probably not going to add pygmies because they’re too small and, as stated, would probably be outcompeted. Might figure out a ten gallon with them someday.
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Hello. My "must have" fish for a community tank would be Sunset or Red Wag Platies.

10 Tanks (Now 11)
It’s also going to be very soft, acidic water, as I’ll be using a RODI system, cut with some tap for minerals. I’ll be aiming for a ph of 6.5 and a hardness of 10 DH.
RODI leads to more problems than it solves. Unless you intend to breed soft water fish, there's absolutely no need for it. I am not aware of any species of fish that cannot happily reside in water with a pH of 8.0 or less. I am also not aware of any species that cannot happily reside in water with a hardness of up to 250 ppm. Most species can handle water with even higher mineral content.
Yeah, but I wish to keep really soft-water tetras like neons, and it’s a Amazon biotope. Also, my water is so hard I can’t actually measure it correctly with the little test tubes: it goes off the chart, and I’m fairly sure it’s somewhere above 300 in GH. Surprisingly, the ph is only at 7.4-7.6
Yeah, but I wish to keep really soft-water tetras like neons, and it’s a Amazon biotope. Also, my water is so hard I can’t actually measure it correctly with the little test tubes: it goes off the chart, and I’m fairly sure it’s somewhere above 300 in GH. Surprisingly, the ph is only at 7.4-7.6
My aquarium is Amazonian also. Your neons are almost certainly farm raised, meaning it's almost certain they were raised in relatively hard water. It's simply too expensive to farm fish using RO water.

I'm keeping wild caught cardinal tetras, and have no issues. I also keep discus, emerald corydoras, and several other varieties of dwarf catfish. No problems whatever. At one time I had wild caught diamond tetras and they were breeding like crazy. I know of at least one discus farm that claims no problems raising discus in water as high as 300 ppm GH. As I said, most species of fish have no problem acclimating to hard water.

I'm assuming you're using API or Tetra test kits? Regardless, if I were you I'd purchase a digital test meter. They aren't expensive and they are more accurate and reliable, assuming you clean the electrodes after each use. They are also much easier to use. As long as your water measures less than 450 ppm, I'd give it a go.
@CherryBerry670 the GH does matter to the well-being of fish, as every knowledgeable biologist will tell you. There are studies proving that lifespan of soft water species is related to the GH, and while some species have the ability to adapt, this is limited and depends upon the species and the values involved.
You might have a problem keeping any fin-nippers with your gouramis. Also, I think they are not compatible with the water parameters of your soft water fish. It will be a tricky balance if you plan to remineralize your RODI water to find the exact place where both types of fishes can comfortably live. Brightwell makes GH, KH and other minerals for treating RODI water to make it appropriate for fishes, both in individual parameter powdered forms and a liquid combination form. That is what I use to give my RODI water what my fish need. If you can create the right parameters using your well water, then good for you. I know the salts used in softening well water is not ideal for watering my houseplants, so I don’t think it would be ideal for my fish either, but perhaps that is just me.

Personally, in a 75 gallon tank, if you like the electric blue dwarf gourami (you didn’t specify which type of dwarf you liked), then you might like the electric blue acara (one of my favorite fishes).

I love setting up a new tank. All the possibilities. Have fun with it.
Oh, I love the acara. They were actually my first choice. They just have big mouths and could likely eat my tetras (Some of the tetras are torpedo-shaped), and I don’t want to sacrifice my fish. I’ve given up on the gourami and decided to go with a really big school of neon tetras for the blue colors and a female Bolivian ram school for the centerpiece.

As for RODI, I’ve brought a mineralizer, Equilibrium, that should get it remineralized to good levels. These are mostly beginner fish, so they should be forgiving, but I’m still pretty sure I can get to a alright level of GH/KH.

And about the GH thing, I’ve tried keeping most of the tetras I like in hard water. Or more accurately, my mom has. All her neons died within days because of it. These are way too expensive to risk it. I want all of my fish to live for as long as they can, since I like bonding with my fish, so I want to keep them in the most ideal conditions.
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This may be a good time to mention something about RO. I've no idea as to your level of experience/knowledge so forgive me if this is old news. But as one who has gone the route of having to prepare water for a couple of issues, it may help you decide.

First, the water for all water changes must be prepared outside the tank. I used one of those large garbage containers, Rubbermaid 30+ gallons. The GH/pH/temperature must be the same as the tank water. Next problem is siphoning it out into the aquarium; with the container likely on the floor, you are restricted to using a bucket or one of those rubbermaid fruit juice pitchers (lidless). This needs to be done for any emergency W/C's too.

Second thing is the fish preferences. If you stay with all soft/very soft water fish, like cories, tetras, gourami mentioned, I would not mess with mixing but just use straight RO. This is basically what they have in their habitats and they have evolved to function at their best in such water. They get what minerals they need from their food. I have been fortunate in my 30 years of aquaria to have tap water that was about as good as it gets to such water, zero GH/KH and a very acidic ph (below 5 so far as I knew). I let the tanks pH do what it wanted, and the biological system established in each tank and readings of pH never fluctuated over months and even years beyond more than a decimal place or two. If however you move to Central American cichlids or livebearers, this is not going to do it obviously.

Third, I used Equilibrium for three or four years in two tanks (the largest). A well-meaning member (another forum) persuaded me it was necessary (the old fable again, fish and plants must have minerals in the water, blah, blah). This was primarily to get sufficient calcium for the plants, given my water purity; the swords did show signs of calcium deficiency. I subsequently switched to using Flourish Tabs for the swords and stopped the Equilibrium. Plants didn't seem to notice, but I was more concerned with the fish. Ian Fuller breeds cories in straight RO. @seangee uses this in his tank(s). It is in my view easier. If you do decide to increase the GH, with the fish again mentioned I would not go as high as 10 dH. Down around 2 or 3 is more than enough, though again zero is even better. Equilibrium is geared for plants, and Seachem answered my direct questions by saying it should not be used for fish, just plants, and if fish need minerals, their Replenish was a better choice. I've no idea why, I certainly did not need any mineralization for any of my hundreds of fish, so I didn't pursue it.

ON the cories, pygmies I always find get lost in large tanks. I don't mean they hide--though they do--but more they are so small you just don't see them much, especially if the other fish are not similar nano size. All cories need sand of course, I think we dealt with that elsewhere. But it is important for their health, very much so.

And in such zero GH water, fish do have fewer issues health-wise. That seems to have been my experience. The three problems I had over the last 20 years were all brought in with new fish and largely my stupidity. Give the fish what they need and they will be better. :fish:
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I agree with not mixing with tap water if you already have RODI. FWIW The DI part is not needed for tropical fish so when the resin is exhausted you can skip it or put in an extra carbon filter which is what I do. As you will already have discovered producing water takes a while. I use 25l plastic drums for the large tank and 10l ones for the small tanks - along with a tap like this. I refill the drums immediately after a w/c but for those tanks where I add minerals I only add it just before I need it. That way I always have plenty of fresh water to hand that can go into any tank should I need it.
Yep, I’ve already got two 5 gallon buckets and a heater for the RO water. I’m planning to store it in small gallon jugs for top-offs, and find a drum that can fit in my closet for water changes. I was figuring I would just get a tall drum and use a Python for WC. I’m planning on buying a 150 GPD RODI system, 7-stage to really murder anything in the water. That should produce at a non-maddening pace.

As for substrate, I was thinking of using plain topsoil, but then realized my corys and pleco and (possible) kuhli loaches would immediately spread it everywhere. So I’m going to use a inch of planted tank substrate capped with about two inches of the black Petco sand.

On GH…I am putting co2 in this tank, so I’m also dosing with extra root tabs and Flourish Trace and Excel, as I usually do. May end up buying the potassium and iron stuff too, but seeing as I’ve always had this exact same duo in smaller distilled water tanks, it most likely won’t be a problem. I think I’ll probably start without the Equilibrium, but if my plants start dying, I’ll add some. Everything I want to keep in this tank is from the Amazon, but I might have to figure out how to add calcium for my snails.

Thankfully, my water is almost perfect for livebearers and cichlids, so if I ever want them that would be easy to set up.

Dang it, no pygmy Cories. I guess I could upgrade my shrimp/betta tank to a ten gallon and add them.
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