2 Gallon (7.5L) Cookie Jar Reef

[StartingATank]

Another macro algae that I find very nice is dragons breath. I’m not sure of its growth rate, but it is very beautiful

 

[kizzy89]

Another macro algae that I find very nice is dragons breath. I’m not sure of its growth rate, but it is very beautiful

Dragons breath doesn't have super fast growth but it splits as it grows so it's easy to put in other aquariums or trade in at LFS. I love it in my 3 gallon

 

[kizzy89]

Dragons breath in the 3 gallon, started with 1 or 2 small ones and now it's almost half the tank.

 

[pietervanwhelp]

It's been a few weeks since I last posted and the cookie jar is still going. No disasters. Cautious optimism.

The coral situation​

Three corals went in a few weeks ago — one zoanthid frag, one mushroom, and a tiny xenia. All three opened up well within the first 24 hours. A few weeks on, I wouldn't say any of them are visibly thriving yet, but they're all holding their color and size which from what I understand is exactly what you want to see in the first month. Nobody's dying, nobody's growing dramatically. Stable is good.

The mushroom drama​

Early on I noticed the edges of the mushroom looked ragged — like something had been nibbling at it overnight. My immediate suspect was the peppermint shrimp but I never caught it in the act. After some trial and error I moved the mushroom to a lower spot in the tank, further from the shrimp's cave. Problem solved — the edge damage stopped and the mushroom has been stable since. Lesson: location matters, even in a 7.5L jar.

The shrimp keeps moulting — apparently that's great​

The peppermint shrimp has shed his exoskeleton a few times now. First time I saw it I genuinely thought something had died. Turns out it's one of the better signs you can get — shrimp only moult when they're comfortable, well-fed, and the water quality is good. I left the shell in the tank each time and the shrimp ate it within a day or two to reclaim the calcium.

CUC still busy​

The cerith has been doing laps of the rock and glass nonstop. The nassarius pop out of the sand when food hits the water, then disappear again. Everyone doing what they're supposed to do.

I started dosing​

Parameters started drifting after the corals went in — magnesium and KH both dropped slightly. I'm now dosing a small amount of Tropic Marin All-For-Reef daily to maintain calcium, magnesium, and KH. At 7.5L the dose is tiny — under half a ml per day — but it's made a noticeable difference keeping things stable between water changes. Honestly wish I'd started doing this earlier.

Current parameters​

Parameter	Reading	Status
pH	8.2–8.4	Stable
Ammonia	0 ppm	Good
Nitrite	0 ppm	Good
Nitrate	5–10 ppm	Acceptable
KH	9–10 dKH	Good
Calcium	400 ppm	Good
Magnesium	1275 ppm	Good
Phosphate	0.03 ppm	Good

Most stable the parameters have looked since the build started. Dosing is working.

Question for the thread​

How much growth should I realistically expect from zoanthids, mushrooms, and xenia in the first couple of months — and at what point does "maintaining size" tip into "actually growing"? I know patience is the main ingredient here but curious what timelines people have seen at this scale. The xenia I have heard takes over tanks in a few months, so watching that one closely.

Still very much a beginner but it's starting to feel a little less terrifying. Thanks for following along.

 

[PolypPocket]

It's been a few weeks since I last posted and the cookie jar is still going. No disasters. Cautious optimism.

The coral situation​

Three corals went in a few weeks ago — one zoanthid frag, one mushroom, and a tiny xenia. All three opened up well within the first 24 hours. A few weeks on, I wouldn't say any of them are visibly thriving yet, but they're all holding their color and size which from what I understand is exactly what you want to see in the first month. Nobody's dying, nobody's growing dramatically. Stable is good.

The mushroom drama​

Early on I noticed the edges of the mushroom looked ragged — like something had been nibbling at it overnight. My immediate suspect was the peppermint shrimp but I never caught it in the act. After some trial and error I moved the mushroom to a lower spot in the tank, further from the shrimp's cave. Problem solved — the edge damage stopped and the mushroom has been stable since. Lesson: location matters, even in a 7.5L jar.

The shrimp keeps moulting — apparently that's great​

The peppermint shrimp has shed his exoskeleton a few times now. First time I saw it I genuinely thought something had died. Turns out it's one of the better signs you can get — shrimp only moult when they're comfortable, well-fed, and the water quality is good. I left the shell in the tank each time and the shrimp ate it within a day or two to reclaim the calcium.

CUC still busy​

The cerith has been doing laps of the rock and glass nonstop. The nassarius pop out of the sand when food hits the water, then disappear again. Everyone doing what they're supposed to do.

I started dosing​

Parameters started drifting after the corals went in — magnesium and KH both dropped slightly. I'm now dosing a small amount of Tropic Marin All-For-Reef daily to maintain calcium, magnesium, and KH. At 7.5L the dose is tiny — under half a ml per day — but it's made a noticeable difference keeping things stable between water changes. Honestly wish I'd started doing this earlier.

Current parameters​

Parameter	Reading	Status
pH	8.2–8.4	Stable
Ammonia	0 ppm	Good
Nitrite	0 ppm	Good
Nitrate	5–10 ppm	Acceptable
KH	9–10 dKH	Good
Calcium	400 ppm	Good
Magnesium	1275 ppm	Good
Phosphate	0.03 ppm	Good

Most stable the parameters have looked since the build started. Dosing is working.

Question for the thread​

How much growth should I realistically expect from zoanthids, mushrooms, and xenia in the first couple of months — and at what point does "maintaining size" tip into "actually growing"? I know patience is the main ingredient here but curious what timelines people have seen at this scale. The xenia I have heard takes over tanks in a few months, so watching that one closely.

Still very much a beginner but it's starting to feel a little less terrifying. Thanks for following along.

I have both of those types corals. For zoas it depends on the kind. I’ve got two that I just got 3 weeks ago already growing new polyps (one is magician zoa, highly recommend). And two of the smaller variety that have been much slower but I’m starting to see a tiny nub one of them and the other nothing. But overall it’s been pretty fast considering I added them mid June to early July.

The Xenia I got has doubled in size (taller) but so far I’m not seeing a lot of new “stems”. I’ve had it a month.

I spot feed both of them with benepets so that might influence growth idk. But they both seem to be fast growers overall.

 

[StartingATank]

Any updates?

 

[pietervanwhelp]

A few weeks since the last update. Everything is still alive, which at this point feels like a genuine achievement. A couple of things worth sharing.

Growth is slow — but it's there​

The zoanthid, mushroom, and xenia are all holding steady. Color looks good, nothing is retracted or unhappy. But "visibly growing" is probably not the word I'd use yet. From what I've read this is normal in the first couple of months — corals establish before they expand — but I'd be lying if I said I wasn't watching them a little too closely every morning.

The sunlight discovery​

I moved the jar to a spot that gets a small amount of direct natural sunlight for a short window each day. The difference was immediate and kind of shocking — all three corals opened up bigger than I've ever seen them. The zoas in particular looked completely different, fully extended in a way they never do under the clip light alone. The mushroom spread out to almost double its usual size. The xenia started pulsing more actively.

Then the sun moved on and everything went back to "normal" within an hour.

My working theory: the clip light is running 6 hours a day and might not be delivering quite enough PAR, especially through curved glass. The sun filled in the gap instantly.

I'm being cautious about it, as I know the consensus on direct sunlight for reef tanks is somewhere between "proceed carefully" and "don't do it" because it's hard to control, can cause temperature spikes, and can fuel algae blooms. So I'm keeping the exposure short and watching the temperature closely. But the coral response was too noticeable to ignore.

Anyone with experience using natural light supplementally on a small tank, is a short daily window genuinely beneficial or am I asking for trouble?

Chemistry is finally behaving​

After a few weeks of parameter ping-pong I think I've figured out what this tank actually needs. Magnesium is the only parameter that consistently drops, so that's the one I dose for. KH and calcium have been stable without intervention. Keeping it simple seems to be working — one supplement, one problem to solve.

Mystery critters on the sand bed​

Noticed some tiny critters crawling around on the bottom that weren't there before. Moving on their own, seem to be grazing the sand surface. No idea what they are — hitchhikers from the live rock presumably, finally emerging now that the tank has some maturity to it.

Anyone know what these are? Beneficial, neutral, or something to worry about? Happy to describe further if the video isn't clear enough.

Still going. Still learning.

 

[Fish Fan]

Looks like amphipods. If so, those are beneficial good guys, like larger copepods