75% rule

[Jholli90]

I was reading an article that mentioned something called the 75% rule. It means you take your tank size and multiply it by .75
The answer is amount of inches of adult fish you can have in your tank.
So by this rule a 60 gal × .75 equals 45 inches worth of fish that the tank would support.
Has anyone ever heard of this before? How accurate is it?

 

[ihavecrabs]

There is no single rule that should be followed for sizing of fish in tanks. It is much more species dependent and inter-species dependent. For example, one shouldn't have a 8" tank in a 40b.

It is better to do research on what the fishes need to minimize stress and therefore extend their lives. Balance out bottom dwelling, rock dwelling, and water column dwelling species. And when you have an idea for your stock list, post it here and get feedback!

 

[ihavecrabs]

Here is a good resource to post your stock lists and to get recommendations if you are attempting to build a list around a specific species:

https://www.reef2reef.com/threads/n...for-your-tank-post-here-and-well-help.200605/

 

[norfolkgarden]

A safer rule for small fish in small tanks is reserving 7 gallons per 3" fish.

So as long as you structured it with some bottom dwellers and some swimmers you could have 8 or 9 fish that reach 3" in a 60 gallon tank, if your filtration was up to that.

I would only at 2 or 3 at a time at the most.
Start with fish well below their mature size.

 

[mta_morrow]

There is no single rule that should be followed for sizing of fish in tanks. It is much more species dependent and inter-species dependent. For example, one shouldn't have a 8" tank in a 40b.

It is better to do research on what the fishes need to minimize stress and therefore extend their lives. Balance out bottom dwelling, rock dwelling, and water column dwelling species. And when you have an idea for your stock list, post it here and get feedback!

^^^^^Excellent, and the best advice!

 

[Jholli90]

A safer rule for small fish in small tanks is reserving 7 gallons per 3" fish.

So as long as you structured it with some bottom dwellers and some swimmers you could have 8 or 9 fish that reach 3" in a 60 gallon tank, if your filtration was up to that.

I would only at 2 or 3 at a time at the most.
Start with fish well below their mature size.

I think my filtration should be up for it. I have 8 fish picked out. I have a 65 gal, with a 100 gal canister filter. It moves 360 gallons of water an hour. I also have 200 gallons worth of biological filters in the canister along with 3 replaceable medias to change each month... the biologicals I used are the xport bio cubes and matrix. I have 60 -70 lbs of live rock, and a 2 1/2 inch sand bed of live sand. Would this be enough to support my fish? All are 3 or 4 inches except my tomini. He will be the only big one.

 

[Jholli90]

There is no single rule that should be followed for sizing of fish in tanks. It is much more species dependent and inter-species dependent. For example, one shouldn't have a 8" tank in a 40b.

It is better to do research on what the fishes need to minimize stress and therefore extend their lives. Balance out bottom dwelling, rock dwelling, and water column dwelling species. And when you have an idea for your stock list, post it here and get feedback!

I have been using live aquaria as my main research for picking out fish and then coming here for better feedback. Everyone here is always ready to help and not bothered by the million questions I ask lol but I found that article and thought this is crazy advice so I had to know if anyone had heard of it before.

 

[nereefpat]

What are the dimensions of the tank?

What is your potential stock list?

We can help if you give us these. As stated, rules of thumb don't have much merit.

 

[4FordFamily]

No rule exists. 5 inches of tang is very different from 5 inches of cardinal or wrasse. The tang will be 2-3X "dirtier". 5 inches of puffer would be even heavier on the bioload. In short, it depends very much on nutrient export, width, choice of fish (species, size, ability to handle stress, etc), and a plethora of other factors.

I overstock my tanks pretty dramatically but a lot of thought and time goes in to it. I have "plan B" tanks for when fish outgrow my tank or need to be moved (a ~500 gallon total volume wall tank build) and my nutrient export is overkill for most tanks --- but not mine.

 

[norfolkgarden]

I think my filtration should be up for it. I have 8 fish picked out. I have a 65 gal, with a 100 gal canister filter. It moves 360 gallons of water an hour. I also have 200 gallons worth of biological filters in the canister along with 3 replaceable medias to change each month... the biologicals I used are the xport bio cubes and matrix. I have 60 -70 lbs of live rock, and a 2 1/2 inch sand bed of live sand. Would this be enough to support my fish? All are 3 or 4 inches except my tomini. He will be the only big one.

What fish do you have now?

Any tang in less than a 4' tank with at least 75 gallons (and that's still too small) is too much. They really need the swimming room.

They will survive, but you can watch them thrive in a bigger tank.
The difference is noticeable.

That "general rule " I mentioned earlier was only for small mature fish.

It is just a starting point better than "It depends".

As many people have mentioned, you will need to research each individual fish and their specific needs.

Mostly/*only* eats pods,
Needs sand for sleeping,
Need to be fed at least 4 times a day,
Not good with same species,
Not good with aggressive species

Any of these can be more important than the mature size of the fish.
[emoji4]

 

[Jholli90]

My tank is 48"×24"×12"
I already have a mix of snails ( 3 astrea 2 nassaurius 3 turbos 2 bumblebees and 1 margarita) and 5 hermits ( will add more) and 1 cleaner shrimp

My stock list is.
1. Yellow watchman ( already have)
2. Chalk bass (already have)
3. Black combtooth blenny
4. Royal Gramma
5. Melanarus wrasse
6. Flame angel
7. Tomini tang
8. Azure damsel OR blue reef chromis

They are listed in the order I plan to add them, with the exception of #8. I can't decide which one i want, or if I can find a better blue to match my tank. Damsels have a bad rep, but supposedly the azure is the most peaceful. The chromis is a shoaling fish, but everyone says they kill each other anyway and are left with 1. I would add the chromis after my gramma if I chose it, or if I went with the damsel, it would be last.

I am open to suggestions on a vibrant blue fish that is reef safe. I do want to add soft coral eventually.

 

[Jholli90]

Oh, and I wanted to get 1 fighting conch

 

[ihavecrabs]

I do love that size tank but it does come with its challenges. One thing to keep in mind is a 12" tank likely has its water level at 11". If you have sand, that takes the available water column down say to 10". For fish that spend a majority of their time in the water column swimming, this might be stressful (like to Tomini tang.. my opinion of course).

Definitely post your stock list and tank details to the link I provided above and you'll get some great feedback from the experts like @eatbreakfast

 

[mta_morrow]

My tank is 48"×24"×12"
I already have a mix of snails ( 3 astrea 2 nassaurius 3 turbos 2 bumblebees and 1 margarita) and 5 hermits ( will add more) and 1 cleaner shrimp

My stock list is.
1. Yellow watchman ( already have)
2. Chalk bass (already have)
3. Black combtooth blenny
4. Royal Gramma
5. Melanarus wrasse
6. Flame angel
7. Tomini tang
8. Azure damsel OR blue reef chromis

They are listed in the order I plan to add them, with the exception of #8. I can't decide which one i want, or if I can find a better blue to match my tank. Damsels have a bad rep, but supposedly the azure is the most peaceful. The chromis is a shoaling fish, but everyone says they kill each other anyway and are left with 1. I would add the chromis after my gramma if I chose it, or if I went with the damsel, it would be last.

I am open to suggestions on a vibrant blue fish that is reef safe. I do want to add soft coral eventually.

I have 3 Azure damsels, 1 green chromis, 2 ocellaris clowns.

No issues.

The azures are a beautiful fish when healthy and colored up, and very active amongst the rock work.

Having 3, they stay very focused on each other and have never gone after any of my long list of peaceful, small fish.

 

[mta_morrow]

Oh, and I wanted to get 1 fighting conch

Conchs do a good job.

I would recommend however to wait till your mostly stocked and feeding well.

A conch eats like a horse and you may find yourself with a hungry conch that you will have to supplement its food source.

 

[Jholli90]

I do love that size tank but it does come with its challenges. One thing to keep in mind is a 12" tank likely has its water level at 11". If you have sand, that takes the available water column down say to 10". For fish that spend a majority of their time in the water column swimming, this might be stressful (like to Tomini tang.. my opinion of course).

Definitely post your stock list and tank details to the link I provided above and you'll get some great feedback from the experts like @eatbreakfast

My tank is the other way around. Its 48" long, 24" tall with a 12" depth or width (not sure what it would be called)

 

[Jholli90]

I do love that size tank but it does come with its challenges. One thing to keep in mind is a 12" tank likely has its water level at 11". If you have sand, that takes the available water column down say to 10". For fish that spend a majority of their time in the water column swimming, this might be stressful (like to Tomini tang.. my opinion of course).

Definitely post your stock list and tank details to the link I provided above and you'll get some great feedback from the experts like @eatbreakfast

Thank you, I will post the list there.

 

[nereefpat]

In that case, I would treat the tank like a 55 gallon with a couple more inches of height.

I like your list. The changes I might suggest would be:
Skip the tang.
Change the flame angel to a smaller flameback, or cherub or similar.

 

[WVNed]

45 inches of fish is 15 adult clownfish in your tank as a simple example.
So nope the rule doesn't work.

Your biofilter relies on a canister filter. Do you have a spare? If you max out your bioload and rely on equipment to maintain it like a canister filter it will break on a holiday weekend.
What if the power goes out.
Also biofilters have to grow. Add stuff slowly and let it do so.

You are pushing way to hard.

Once there is stuff to eat you figure a CUC by snails per gallon not 5 in a tank. You will need to multiply what you have by ten times to do anything useful.

 

[norfolkgarden]

I would respectfully disagree about the snails.

You current snail list is fine. Except the margarita will die from the heat and the bumblebees are just cool tiny predatory toys.

We have 3 turbo, 3 astrea, a money snail and a few remaining hermit crabs.

Nitrates and phosphate through the roof and no algae problem.
(Just a softy/LPS tank.)

We use GFO to export/limit phosphate and 10 to 15 gallon/week water changes to export/limit nitrates.

Snails just eat it and poop it back out.