Stocking a 100 gallon?

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Aquarium Advice Newbie
Oct 29, 2023
Hi all!
I'm very new to the hobby, and although I've been doing a lot of research I'd love to get the opinion of more experienced fish keepers on my first aquarium.
I have a 400 liter (100 gallon) aquarium at 24°C with a pH of 7.2, and I plan on having it moderately/heavily planted (depending on how well it goes lol) with a substrate of river rocks capped with a thick layer of sand with root tabs under the plants that need them. It has a 1000 liter per hour canister filter and I plan on adding a sponge filter to help with filtration, oxygen and water flow. I'll start with just a couple white cloud mountain minnows, but the stocking I am thinking of building up to is:
3 hillstream loaches
6 otocinclus affinis
6 corydoras
~20 white cloud mountain minnows
~10 Pseudomugil gertrudae
10 kuhli loaches
And some Malaysian trumpet snails to help stir the substrate.
Does this sound ok? I checked with aqadvisor and it said my stocking level is at 78% and I have a filter capacity of 270% with this stocking, though I am more concerned about compatibility. From what I've read all these species are peaceful and shouldn't have any problems together, but there may be something I've overlooked in my research.
Thanks for reading my wall of text, and I would be happy to listen to any advice or suggestions!
It seems a bit of a waste of a 100 gallon tank if im honest. I would want either some bigger fish or bigger schools of small fish. A tank that size might look a little empty, especially with so many bottom dwelling fish that are going to spend most of the day hiding.

24c is a little on the warm side for WCMM. They will survive, but its not ideal for them and they possibly wont live out their normal expected lifespans.

You might want to let the tank run for a couple of months for the algae/ biofilm to build up a little before adding the otos.

You might find the loaches outcompete the corys for food.

You probably dont need any additional filtration more than the canister, especially with such a small stock level. What canister do you have? You may want to add in a powerhead to give you plenty of water circulation and prevent deadspots at the far end of the tank from the filter.

Your sand wont stay as a capping layer. It will find its way into the voids between the river rocks and just get lost. Smaller particle substrate will always find its way to the bottom and the larger particles to the top. If you want the visual appearance of sand, just go for sand.
Thanks for the insight! The tank has been running for a long time, it used to house turtles and I haven't turned the filter off since, and I'm waiting a few weeks anyway for the plants to settle in before adding any fish.
I already have the river rocks from when I had the turtles, and the thought was to add in sand so the loaches and corys would have it while keeping the river rocks so the plant roots have space to grow and so the sand doesn't get too compact.
I'm not sure of the exact kind of filter since it was bought second hand, it looks like a SunSun HW-302 external filter from comparing it to the ones I found online.
Would it be reasonable to try and get the corys and loaches used to getting fed on opposite ends of the tank to lessen competition, or is it better just to choose one to keep?
As for the white clouds, do you have any suggestions of a better schooling fish to fill the space? How big of a school do you think I would need? The problem I encountered most the time while looking for other options was that many were either aggressive or preferred warmer water.
Sunsun buy their filters from a manufacturer and put their branding on them. Other brands do the same, so you get identical filters with different brands on them. All-pond-solutions and polar aurora are other brands that have identical filters all made by the same manufacturer. Im sure there are others. If yours is the one rated to turn over 1000 litres/ hour then its the one you have quoted or an equivalent by a different brand then id say its good for upto a 50 gallon tank, so i agree with your original thought of needing some additional filtration. Why not another canister?

If you want a sand substrate then just take out the river rocks, and use them to create some features on your sand substrate. River rocks on their own will just trap uneaten food, that will decompose and cause you water quality issues.

Khuli loaches in particular are nocturnal fish and will do their feeding at night, looking for uneaten food on substrate. Corys are diurnal, they will be active when there is food about, but prefer to be out at night also scavenging for the same uneaten food. Its not like you feed one at one end and the other at the other end. Personally, id pick one or the other, but you do have a large tank where they can each find their own space so it might work out.

Im not really a fan of recommending fish because you end up with what i would keep rather than what you want. Most tropical fish are fine at your water conditions. Tetras, barbs, most danio species, are good fish that are social and like to be kept in groups. Most fish arent schooling fish. They like to be kept in groups but dont often school. Schooling is a defence mechanism, and they do this when they feel threatened. Schooling behaviour is a sign they are feeling stressed.

If you wanted a similar fish to WCMM that would be better at slightly higher water temperature, then maybe glowlight danios (not to be confused with glofish danios).

For how many social fish, 6 is usually considered a good minumum, ideally 10, but always more is better as long as the tank can accommodate them. Apart from what ive just read i dont know anything about those small rainbow fish, but in your size tank i would look at individual groups of 20 to 25 fish if you plan on keeping them with a species of minnow/ danio, or 50 if you plan on keeping one species of social fish.

If the tank no longer has anything living in it, expect the cycle to crash. The microbes responsible for the nitrogen cycle will grow or recede depending on the amount of food/ waste (ammonia) is available to them. If there is nothing producing ammonia then these microbes will slowly die off, and then when ammonia producing creatures are again added it will take a little while to grow back. So i would keep the filter running to slow down the die off, and get some fish in the tank as soon as you are able.
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I was thinking of going with a sponge filter instead of a second canister for the added benefit of extra oxygen since I don't have an air stone. Is a second canister filter instead that much of an improvement? I could put the output of the current filter above the water level for a mini waterfall to create surface agitation but since the tank is so tall I was worried it might not be enough.
Thanks for the suggestion of glowlight danios, I hadn't heard of them before but they look rather nice, I'll look into them!
As for the cycle I've been adding turtle food every now and then to try to keep it alive, but I'll keep that in mind when it comes time to add the fish.
A canister filter will give you great oxygenation if you set the outlet below the waterline but aim it at the surface so you get surface agitation. A sponge filter will work, its going to be very cost effective, but one thats going to give you filtration for that 50 gallons is going to be fairly big and might detract from what you want to see in the aquarium. Its up to you.

If you went down the additional canister filter route, i would take half the filter media from your old filter and add it into the new filter then top them both up with new media so that both filters have some cycled media in them, and the new media can seed from the established media.
Fwiw we have a 125g cichlid setup here. Currently running a fluval fx4 canister, a fluval cp4 powerhead and a maxi-jet 1400 powerhead. The canister is outputting down lower in the tank and I have a powerhead at each end aimed up for surface agitation. Long term, we will be adding an fx6 canister and taking out the maxi jet as its just unsightly. I love the idea of running dual canister because 1) i can alternate cleaning of them without massively disturbing media and 2) i will have 5 different baskets to custom tailor my filtration needs. In my experience you dont really need to "break" the surface as in a wayerfall type situation so much as you want ripples/waves across the surface.
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