Stocking Advice for a 180l Trigon

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Aquarium Advice Newbie
Jun 26, 2023
Hi All,

I have a lovely stocked tank, it's been up an running for a year now with perfect water conditions and a reasonably stable stock, but I do have a couple of issues I just have never been able to resolve. Over the year I have tried to play around with adding stock, but after a few weeks of everything looking good gradually the new stock dies off one by one, usually 2-3 weeks apart. eg Phantom tertras I tried adding 6 and they were fine for 8 weeks, then over 3 months died off.

Trigon 180l
Fluval 307 canister filter
Water changed of 40l once a week
Lots of wood and rocks for hiding
8:30-15:00, then 16:30 to 20:00Lights on for total 10 hours per day
Feed 6 days a week. Generally pinch of flakes, 2 wafers and a block of frozen bloodworm/daphnia/tropical quarter

Current stock:
3 Silver Dollars. (Full grown and healthy)
1 Opaline Gurami (Full grown and healthy)
5 Platys (Full grown and healthy)
7 Cardinal Tetras (Full grown and healthy)
2 Black Neon Tetras (Full grown and healthy)
1 Opaline Gurami (7 months old, but looks a little bullied and stuck 60% growth.

1 x Bristlenose Pleco (Full grown and healthy)
1 x Gold Bristlenose Plec (6 months old, growing well)
a few other bottom feeders, all been stable for a year
1 x African Shrimp, 6 months old looking good
1 apple snail - awesome and I love it.

Am I at the limit of stocking? Anything I can add in to add colour? Or is stocking messed up? I am much more concerned with healthy tank than pretty tank.

Question 2:
Every time I add plants they either get eaten or die. Javas get black spots and die (I have tried dosing increasing amounts of plant food and liquid CO2 but nothing seems to help.) All other plants just get muched.

Question 3:
I found 2 baby platys 3 weeks ago. Then another one today. I have put them in a breeding net, how long should I keep these in there for?

Sorry for the wall of text, but I really just want to get my tank a little more colourful if possible with plants and fish, but don't want to ruin anything.
Hi and welcome to the forum :)

What is the GH (general hardness), KH (carbonate hardness) and pH of your water supply?
This information can usually be obtained from your water supply company's website (Water Analysis Report) or by telephoning them. If they can't help you, take a glass full of tap water to the local pet shop and get them to test it for you. Write the results down (in numbers) when they do the tests. And ask them what the results are in (eg: ppm, dGH, or something else).

Platies do best in water with a GH (general hardness) around 200ppm and a pH above 7.0. The rest of your fish do well in water with a GH below 100ppm and a pH between 6.0 & 7.0. Black phantom tetras prefer softer water too (GH below 100ppm).


I wouldn't add anymore fish to the tank.

Gouramis are territorial and blue, opaline, gold, 3 spot are the same species and one of the more aggressive gouramis. If you have 2 males, the bigger one will eventually kill the smaller male. Male gouramis have longer pointed dorsal (top) fins, females have short rounded dorsal fins. If you post a picture of the gouramis, we should be able to sex them for you.

Silver dollars are vegetarian and any plants you put in their tank will be eaten. You can supplement their diet with cucumber, zucchini, pumpkin, spinach and marine algae (available from Asian supermarkets or the Asian food section of a normal supermarket). Just make sure anything you feed them is free of chemicals and has been washed well under tap water. You can blanch (partly cook) the fruit and veg to soften them up. Some fish prefer them raw, others prefer blanched.


Plants do best with a continuous photoperiod each day. Having a dark period in the middle of the day will mess them up and can stuff up the fish's circadian rhythm. Just have the lights on from 8am-10pm or whatever time you want but keep the lights on all day.

Don't use liquid carbon supplements for plants. they are normally made of glutaraldehyde, which is poisonous to all living things. Most aquariums don't need supplemental carbon dioxide (CO2) because they get a steady supply from the fish, filter bacteria, and through the air coming in contact with the water. If you only have a few small fish and lots of fast growing true aquatic plants, and they get lots of bright light and loads of fertiliser, then you might need to add CO2, but most tanks don't need it. And you have a lot of fish in the tank so won't need it.

If you post pictures of the plants we might be able to offer more advice on them.


Baby fish should stay separated from the adults until they are at least half the size of the biggest fish in the tank. If you put small fish in a tank, they could be eaten.

Stress from tank lights coming on when the room is dark can be an issue. Fish don't have eyelids and don't tolerate going from complete dark to bright light (or vice versa) instantly.

In the morning open the curtains or turn the room light on at least 30 minutes (or more) before turning the tank light on. This will reduce the stress on the fish and they won't go from a dark tank to a bright tank instantly.

At night turn the room light on and then turn the tank light off. Wait at least 30 minutes (or more) before turning the room light out. This allows the fish to settle down for the night instead of going from a brightly lit tank to complete darkness instantly.

Try to have the lights on at the same time each day. Use a timer if possible.

If the light unit is programmable, have it on a low setting for the first 30-60 minutes and increase the brightness over time. Do the opposite in the evening and gradually reduce the light for the last 30-60 minutes before lights out.

If you don't have live plants in the tank, you only need the light on for a few hours in the evening. You might turn them on at 4 or 5pm and off at 9pm.

If you do have live plants in the tank, you can have the lights on for 8-16 hours a day but the fish and plants need 8 hours of darkness to rest. Most people with live plants in their aquarium will have the lights on for 8-12 hours a day.


Most aquarium plants like a bit of light and if you only have the light on for a couple of hours a day, they struggle. If the light doesn't have a high enough wattage they also struggle. Try having the tank lights on for 10-12 hours a day.

If you get lots of green algae then reduce the light by an hour a day and monitor the algae over the next 2 weeks.
If you don't get any green algae on the glass then increase the lighting period by an hour and monitor it.
If you get a small amount of algae then the lighting time is about right.

Some plants will close their leaves up when they have had sufficient light. Ambulia, Hygrophilas and a few others close their top set of leaves first, then the next set and so on down the stem. When you see this happening, wait an hour after the leaves have closed up against the stem and then turn lights off.

Plant lights should have equal amount of red and blue light and a bit less green light.


If you have two light units on the tank, put them on timers and have one come on first, then an hour later the second one can come on. It will be less stressful for the fish.

In the evening, turn the first light off and wait an hour, then have the second light go out.

If the lights have a low, medium and high intensity setting, have them on low in the morning, then increase it to medium after a couple of hours, and then high for the main part of the day. In the evening, reverse this and have the medium setting for a few hours, then low. Then turn the lights off.


Some good plants to try include Ambulia, Hygrophila polysperma, H. ruba/ rubra, Elodia (during summer, but don't buy it in winter because it falls apart), Hydrilla, common Amazon sword plant, narrow or twisted/ spiral Vallis, Water Sprite (Ceratopteris thalictroides/ cornuta).

The Water Sprite normally floats on the surface but can also be planted in the substrate. The other plants should be planted in the gravel.

Ambulia, H. polysperma, Elodia/ Hydrilla and Vallis are tall plants that do well along the back. Rotala macranda is a medium/ tallish red plant that usually does well.

H. ruba/ rubra is a medium height plant that looks good on the sides of the tank.

Cryptocorynes are small/ medium plants that are taller than pygmy chain swords but shorter than H. rubra. They also come in a range of colours, mostly different shades of green, brown or purplish red. Crypts are not the easiest plant to grow but can do well if they are healthy to begin with and are not disturbed after planting in the tank.

Most Amazon sword plants can get pretty big and are usually kept in the middle of the tank as a show piece. There is an Ozelot sword plant that has brown spots on green leaves, and a red ruffle sword plant (name may vary depending on where you live) with deep red leaves.

There is a pygmy chain sword plant that is small and does well in the front of the tank.


Lots of plants are sold as aquarium plants and most are marsh plants that do really well when their roots are in water and the rest of the plant is above water. Some marsh plants will do well underwater too.

Hair grass is not a true aquatic plant, neither is Anubias.

Some common marsh plants include Amazon sword plants, Cryptocorynes, Hygrophila sp, Rotala sp, Ludwigia sp, Bacopa sp. These plant do reasonably well underwater.

True aquatic plants include Ambulia, Cabomba, Hornwort, Elodia, Hydrilla and Vallis.

The main difference between marsh plants and true aquatic plants is the stem. True aquatics have a soft flexible stem with air bubbles in it. These bubbles help the plant float and remain buoyant in the water column.

Marsh plants have a rigid stem and these plants can remain standing upright when removed from water. Whereas true aquatic plants will fall over/ collapse when removed from water.


If you add an iron based aquarium plant fertiliser, it will help most aquarium plants do well. An iron based fertiliser is not just iron, it contains other nutrients as well, but the main ingredient is iron. The liquid iron based aquarium plant fertilisers tend to be better than the tablet forms, although you can push the tablets under the roots of plants and that works well.

You use an iron (Fe) test kit to monitor iron levels and keep them at 1mg/l (1ppm).

I used Sera Florena liquid plant fertiliser but there are other brands too.


There is no point adding carbon dioxide (CO2) until you have the lights and nutrients worked out. Even then you don't need CO2 unless the tank is completely full of plants and only has a few small fish in or no fish in it.

There are no natural waterways anywhere around the world that have supplemental CO2 added to them to make aquatic plants grow. People add CO2 to aquariums to help some marsh/ terrestrial plants grow underwater. These plants should not be grown in aquariums and the fact they need to add CO2 (as well as huge amounts of fertiliser and light) just to keep them alive is a clear indication they shouldn't be kept underwater.

In an average aquarium, there is a constant source of carbon dioxide produced all day and night by the fish, and the bacteria in the gravel and filter. More CO2 gets into the aquarium from the air mixing with the water. And plants release small amounts of CO2 when resting. There is no real need to add CO2, either in a gas or liquid form to an aquarium unless it is devoid of fish. There is plenty of CO2 in the water in most aquariums.

Liquid CO2 boosters often contain Glutaraldehyde, which is a disinfectant used to clean and sterilise medical equipment. It is highly toxic to fish and other aquatic organisms and people have wiped out tanks by adding too much of it. These products should not be used for aquariums.

For aquarium plants to use supplemental CO2, they need lots of light and lots of nutrients. Unless they have the light and nutrients, they won't use a lot of CO2, so there's no point adding extra. To check if your plants are getting lots of light, see if any of them produce streams of tiny little bubbles from their leaves. This is called pearling and is the plant photosynthesising and producing tiny bubbles of oxygen. Algae also does this when given bright light and nutrients.


Some pet shops sell aquatic plant substrates that are meant to improve plant growth. Most don't do anything except add a lot of ammonia to the water and eventually turn into a brown mud on the bottom. Since the majority of aquatic plants take in the nutrients they need via their leaves, having a plant substrate is not going to help much. There are exceptions to this and laterite (red clay) can sometimes be added to the gravel to increase the iron level for the plants taking in nutrients via their roots. But for most plant tanks, all you need is gravel on the bottom of the tank.

Most aquatic plants need at least 2 inches of substrate to grow in and some need 3-4 inches.
Thanks for both those posts, very informative!

So first thing I have done is stopped the lights cycling, they are now 8-8. And stopped the CO2 dosing. I will get a pic of the plants later today.

I just found a dead platy this morning, tested water and Nitrates, Ammonia etc are all 0 or as close as can be. PH I have run out of tests, but it was middle of acceptable range, I will try to get more tests today.

Could it just be the gourami? Should I give up on it (beautiful as it is) and sell/give away that one fish? I can't think of any other reason I just get such a gradual steady drip feed of smaller fish dying.
Post pictures of the dead platy and the remaining fish so I can check them for disease. Also a picture showing the entire tank might offer ideas too.

Do any of the fish show symptoms or act unusual just before they die?

If you can post a video of the fish showing the gourami and how it interacts with the other fishes, that might offer some ideas.
You can upload videos to YouTube and then copy & paste the link here. Make the video about 2 minutes long.
If you use a mobile phone to film the fish, hold the phone horizontally so the footage fills the entire screen and doesn't create black bars on each side.
Thanks again. Unfortunately I disposed of the dead fish this morning. I could not see any white spot, bloating or injuries on it though. It tends to be one fish every 2 weeks or so.
I have no idea why (hence my request for help) but I suspect stress or bullying.

Here is the tank:

You can see the plants that keep dying off. All the fish look okay to me, but again I am obviously missing something.
If you've had the albino cories dying, it's possibly due to the substrate.

Them stones can't be doing their barbels much good, which will lead to their barbels getting damaged and possibly infected. They find food using them and when they get damaged, it's harder for them to find food.
In the video, it seems you're well stocked. Some largish fish in there.

If in doubt, check the AqAdvisor website. If you're unsure, post the tank dimensions and I'll take a look.

The lighting didn't seem overly bright, so that might be your plant issue.

Bare in mind that when plants decay, it produces ammonia, could have caused previous deaths.

It might be worth checking what plants grow well with pebbles too. You might need to stick to rhizomes that stay out of the substrate. (I've not used pebbles but when I think, when I've seen a pebbles in a stream, I don't think I've seen much plant life) although, that could be because nothing can grow from underneath. If you're placing it in there yourself, it might grow.

Have you ever tried hornwort? That's generally easy to grow and doesn't need substrate.

The other plant that might look good for you is subwassertang. I bought some last night, waiting on delivery. It's German for "freshwater seaweed".
So I spent 5 mins, estimated your tank dimensions so it went to 177 litres.

Probably worth doing it yourself properly.

You're stocking level is 146% according to AqAdvisor (didn't add the bottom feeders or snails etc). The silver dollars being the main culprits, especially as they are supposed to need a bigger tank and in a bigger group.

You're probably getting away with it right now as not all are fully grown, but you might well have further issues once they are.AquStockImage%20(2).jpg
If you've had the albino cories dying, it's possibly due to the substrate.

Them stones can't be doing their barbels much good, which will lead to their barbels getting damaged and possibly infected. They find food using them and when they get damaged, it's harder for them to find food.

The bottom feeders have been fine. When I got the tank most of the stock was as is, it just the platies and tetras that die. I haven't had a bottom feeder die since I started. But point taken on the substrate. I am tempted to replace so I can plant tank, I will have a look.
The plants are Java fern and they don't need bright light. They have some bite marks on them, probably from the silver dollars, which are vegetarian. The Java fern appears to be tied to driftwood, which is how it should be grown (with the rhizome above the substrate).

You can't have a plant tank with silver dollars, they will eat everything.


Platies from Asian fish farms regularly have intestinal worms and gill flukes. These parasites can kill fish slowly over months and the fish die without any external physical damage. You could try deworming the fish and see if it helps.

One of the platies appears to have a slightly clamped dorsal (top) fin but was moving ok. Clamped fins can be from poor water quality (unlikely considering everyone else was fine) or an external protozoan infection. If the fish doesn't rub on anything then it was probably just clamped for the video and isn't an issue.


Keep an eye on the fish and if anymore look off colour or die, photograph them in the tank and maybe out of the tank as well (on a piece of white paper towel) and I will check them.


If you want to try deworming the fish, see below.

Intestinal Worms like tapeworm and threadworms cause the fish to lose weight, continue eating and swimming normally, and do a stringy white poop. Fish can do this for months and not be too badly affected. In some cases, fish with a bad worm infestation will actually gain weight and get fat and look like a pregnant guppy. This is due to the huge number of worms inside the fish.

Livebearers like guppies, mollies, swordtails & platies are regularly infected with gill flukes and intestinal worms. If the fish are still eating well, then worms is the most likely cause.

You can use Praziquantel to treat tapeworm and gill flukes. And use Levamisole to treat thread/ round worms. If you can't find these medications, look for Flubendazole, which treats both lots of worms.

In the UK look for:
eSHa gdex contains praziquantel that treats tapeworm and gill flukes.
eSHa-ndx contains levamisole and treats thread/ round worms.
NT Labs Anti-fluke and Wormer contains flubendazole.
Kusuri wormer plus (contains flubendazole) - sold mainly for discus, comes as a powder which is quite hard to dose in smaller tanks
Sera nematol (contains emamectin)

Remove carbon from filters before treatment and increase aeration/ surface turbulence to maximise oxygen levels in the water.

You treat the fish once a week for 4 weeks. The first treatment will kill any worms in the fish. The second, third and forth treatments kill any baby worms that hatch from eggs inside the fish's digestive tract.

Treat every fish tank in the house at the same time to prevent cross contamination.

You do a 75% water change and complete gravel clean 24-48 hours after treatment. Clean the filter 24 hours after treatment too.

Do not use the 2 medications together. If you want to treat both medications in a short space of time, use Praziquantel on day one. Do a 75% water change and gravel clean the substrate on day 2 & 3. Treat the tank with Levamisole on day 4 and do a 75% water change and gravel clean on day 5, 6 & 7 and then start with Praziquantel again on day 8.

The water changes will remove most of the medication so you don't overdose the fish the next time you treat them. The gravel cleaning will suck out any worms and eggs that have been expelled by the fish. Repeating the treatment for 3-4 doses at weekly intervals will kill any worms that hatch from eggs. At the end of the treatment you will have healthier fish.
The bottom feeders have been fine. When I got the tank most of the stock was as is, it just the platies and tetras that die. I haven't had a bottom feeder die since I started. But point taken on the substrate. I am tempted to replace so I can plant tank, I will have a look.
Before you do anything drastic like that, definitely do all research prior. The substrate is a lot more than a floor for the fish and means alot to the eco system. It would be an awful lot simpler and safer to find plants that work with your parameters.

The overstocking is probably the No1 priority though
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