I am having trouble deciding whether my existing tank has finished its mini-cycle and is ready to have some new fish.

The 100l tank with running rena XP2 filter is currently empty. I had a beautiful 5 year old black moor in there until two days who when he died *snif snif*. Unfortunately it was my own stupid fault - on the last water change I did on 21st March, I removed the crystal filter sachet, realised I didn't have a new one to replace it with and just ordered a new one thinking the tank would be ok for a few days till it arrived. Kicking myself now, as before I knew it he was behaving oddly.

I then checked ammonia which was 0, nitrite which was 0 and nitrate which was quite high, so I spent a few days doing some partial water changes and adding a bit of salt. He still went downhill, so I re-tested for ammonia which was 0, and nitrite which had now shot up to around 5.0ppm or above! I spent the last 2-3 days of his life frantically doing huge water changes and adding more salt (to around 3g/litre) plus the new filter sachet which had arrived by then, plus the old sachet I fished out of the bin. It just wasn't enough though and the nitrite kept rising.

What confuses me is that ammonia never did (and still doesn't) show anything above 0 - could my API testing kit be old and not reading it properly?! I had thought that in order for nitrite to shoot up there must first be ammonia. I understand the basics of cycling but I don't understand this spike.

At first I wasn't going to get any more fish I was so upset and angry at myself - I was going to sell my tank. But going through my kit I realised I enjoy keeping fish so much and have all this knowledge & equipment it would be a shame to give up.

I don't think my black moor had any parasites or bacterial infections. He did sometimes have white stringy poos over the last two years, however he never displayed any other symptoms so I think this was just constipation/poor digestive system. My aim is to not do a through bleaching/cleaning of the tank but to to just get it to finish its cycle before adding 15 neon tetras and 5 guppys (if these do ok I might add 3 blue platys and 2 dwarf gouramis). I used the calculator at aqadvisor.com to calculate the stock, but if anyone thinks this would be too many fish let me know.

Yesterday I did around an 80% water change to get rid of most of the salt, cleaned the sides and given the gravel a good hoover. I also gave the filter a light clean (just removed any waste build-up) and have bought 8 new plants to add to the java fern on bogwood which was already in there. I also added an ornament I had in storage which I used to have in there about a year ago (with two big fancy goldfish in there I had to keep removing stuff to make room!).

My ammonia and nitrite readings today are 0, and nitrate is low, so it LOOKS like the tank has stopped its mini-cycle or spike and might even be ready for new fish. However, I am worried that since the tank has gone through such a lot of changes lately there won't be much of the beneficial bacteria in there and therefore the tank might need to be cycled again (by adding fish food to start it off) before introducing new fish. I am nervous about adding the new fish in case they produce so much ammonia that the tank can't keep up and they all die.

To recap, the new things in the tank which won't have any beneficial bacteria on them yet:

- Crystal filter sachet (3 days old)
- 8 new plants
- Ornament
- Filter output tap (i exchanged the single tap for the punctured tube type - might be gentler for the small fish)
- Heater

I also removed a few things yesterday which I decided I didn't like much or need:

- 3 large smooth pebbles
- 2 old plants
- Feeding dish

The gravel, bogwood, filter inlet tube, airstone and the rest of the filter are all the same so I guess there is still some of the old bacteria in there. I don't know how quickly the bacteria will colonise the new surfaces.

I haven't been adding any fish food to the tank since my moor died - should I have been doing this to keep the cycle going?! I read on the fishless cycling guide (http://www.fishkeeping.co.uk/articles ... hless-cycling-article.htm) that you are meant to keep adding food to keep ammonia at 3ppm until the nitrite rises and then starts to fall.

My basic question is this - if the ammonia and nitrite stay at 0 for the next few days, do people think this means the tank is ready for new fish? Or should I kick off a cycle using fish food and wait until it completes and then add new fish?

I feel I need to take a degree in chemistry to understand all this!

I've attached a pic of the new tank. Sorry for the longwinded post, any advice would be much appreciated!

Thank you!!

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Its possible that the ammonia eating bacteria were happily surviving, but that you had a die-off, (or perhaps never very many) of your nitrite eating bacteria.

What other filter media do you have in the filter?

The Crystal Sachets are chemical and mechanical filtration, but don't really do much in the way of biological filtration (they'll provide a surface area for bacteria to grow, but if you're replacing them each month you'll be pulling them out as soon as their numbers get up to a decent level. Most people either don't use chemical filtration at all, or to deal with specific problems- Carbon to remove medications, dedicated nitrate and phosphate removers, etc.

Personally I'd buy some biological noodles or similar (Eheim SubstratPro is good, but expensive, I use a mixture of Fluval and AquaOne's noodles). In the meantime take the Crystal Sachet out, and add either pure ammonia (preferable) or fish food, and see if your bacteria have survived. Some may have done, but if its been a week since the Moor died, and you've not been putting an ammonia source into the system then you've probably had a die-off and will have to start the cycle again.

In terms of stocking I tend to follow the 1" per gallon/ 1cm per 2.5L rule. This generally leads to understocking a tank. That would give you enough space for about 40cm of stock- 10 neon tetras or a similar sized fish. Depending on your nitrates you could increase your stock a little.

Personally I'd not mix neons and livebearers. Neons (and gouramis) prefer soft acidic water to thrive, whereas livebearers like hard alkaline water. You report your pH as 7 and your hardness as 210-320. Where do those figures come from? With hard water I'd expect your pH to be higher than 7 if left for 24 hours.

Hello, thank you so much for your reply!

My black moor died and was removed from the tank on Monday afternoon, so only 2-3 days ago. I change the crystal sachet every 6 months or so as I realise the manufacturer's reccomendadtions are a bit too frequent. I have bacti-stars in the XP2 (about 6-8 of them from what I remember) and I try and change a few of these every 6 months or so. I also have a rena 20ppi pad and a rena 30ppi pad, and a white poly filter pad (imitation Rena type). I use seachem prime with every bucket of fresh water when I do water changes.

Shall I start adding food until I see it reach 3ppi and follow the fishless cycling guide to the letter until it has done a full cycle?

Regarding the new stock, I will have to think some more about that. The hardness reading I have got from asking my water company for the figure. I know the water here is quite hard, so sounds like it would be ideal for guppys.

I think I probably took the ph reading from fresh tap water before, so I've just done a reading from the tank water which has been sitting for about 24 hours and it's higher - at least 7.6 (my API tester card ends at 7.6, so it could be higher). Image attached!

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I just had a thought - if my LFS is keeping their neon tetras in hard water would this mean they might do ok in mine? I might ask them what their ph is next time I go in.

No it doesn't. Remember fish at the LFS are there temporarily; it's not meant to be a home for life, which should be closer to their natural conditions. Fish kept long term outside their range of tolerance for water hardness, pH or temperature fail to thrive, live shorter lives on average, are more susceptible to any illness or infection and usually don't look as good as they ought to either.

As for the state of the cycle in the tank, you do need to have a reasonable level of ammonia present and monitor how long it takes to disappear, along with the nitrites that will follow it, to be sure the tank is cycled.

You need to get a high range pH test and find out what your true pH is before choosing fish.

Your XP2 sounds pretty empty. Most people cram as much filter media into externals as they possibly can. I have media from two filters I'm not currently using in mine so I can set up new tanks if necessary.

There's no point in replacing the bacti-stars. They do the same job as bio-noodles and the other biological filtration media, providing a surface area for your bacteria to grow on. Fill the tank with as many as you can. Conversely with the chemical filtration (crystal sachets) I would be inclined to follow the manufacturer's instructions as they will become exhausted. The zeolite only has so much adsorbative power before it has to be replaced. 6 months might be pushing it.

What Dave said; and something he didn't mention.. DONT THROW AWAY THE BACTI STARS AFTER 6 MONTHS!! These things, like noodles last for yyeeeeeeaaaarssss.

Hehehe ok, I won't throw the stars away! I'll cram some more in there.

I understand about the tetras - thank you for the advice, I had better avoid them and similar ones for my tank. I've ordered a high range ph tester, so will test again with that when it arrives. In the meantime if the ph is ok for them all, I am thinking:

5 guppys
3 blue platys
1 mollie

Does this sound reasonable for my tank size?

I've also ordered some Kleen Off ammonia to start the cycle off properly, and some more bacti stars to fill that compartment of the filter completely. I have also just realised I should have been using an extra two black foam pads in the filter, so it now has 4 black pads. Not sure how this escaped my attention before..

Hi

If the water is hard and alkaline (as seems likely) it should suit those fish choices, but there are a couple of minor issue to consider. Mollies and Guppies kept in the same tank have beeen known to interbreed and produce hybrid offspring, which is something you'd be better off avoiding as hybrids are often weak and hybridisation is something we try to avoid in the hobby generally. Because they are both prolific breeders you'd need an outlet to pass on some of the young and while some shops will take excess fry (but not all will), they won't want hybrid youngsters. It would be better to stick with the Platys and either Guppies OR Mollies. I don't think you've said what the length of the tank is but Mollys need at least 3 feet in length, so if it's smaller than that, get the Guppies.

A rough guide to stock levels is one inch of fish (at adult size) per gallon initially, rising to 2 inches per gallon as the tank matures if all levels are satisfactory. Your 100 litre tank will hold around 90 litres of water taking account of gravel, decor etc, which is about 20 gallons.

Male Platys are 2 inches long and females are 3 inches and need to be kept as 1m:2f for harmony Guppies need a similar male:female ratio and average 2.5 inches. Mollys are quite a bit larger with males at just over 3 inches and females close to 5 inches long.

You could start with 1 male and 2 female Platys and 2 male plus 4 female Guppys which would bring you up to your initial limit. If opting for Mollys instead of Guppys you could start with 1 male and 2 female Platys plus 1 male and 2 female Mollys and be just slightly over for initial stock, but should be OK if the tank has the length Mollys need.

Hi Fishlady,

The outside measurements for my tank are 91cm long x 31cm deep x 50cm high, so perhaps would be just about long enough for mollys? I think 20g is about right for the actual quantity of water in there.


I'm not so sure I want to breed fish yet so I was thinking of going for all male fish to start with, but that's a good point to remember about crossbreeding, I hadn't ralised they could do that! Will they all be happy being all males? If so, since the males tend to be a bit smaller and I feel one molly might be a bit lonely, do you think this lineup would work?..

- 5 male guppies (total 7.5")
- 3 male blue platys (total 6")
- 2 male mollys (total 6")

Once the tank is cycled would you advise adding all of the new fish at the same time, or adding maybe just the guppys and seeing how they do first? I don't want to overload the bacteria.