Starting Again (almost)

The first thing to advise you is to keep a close eye on your ammonia and nitrite levels, at least once a day, and do a water change if either of them show above zero.
Because the only fish in the tank for several weeks were two bristlenoses, most of the bacteria you used to have in your filter will have died off, leaving just enough to deal with the waste from the bristlenoses. You have just added six mollies, a substantial increase in the bioload, and it's going to take a while for the bacteria to multiply enough to cope with all the waste from the now eight fish. I would suggest you reduce the amount of food you feed until the filter has caught up (ie zero ammonia and nitrite) then increase again to what you would normally feed.

You'll need to wait until your ammonia and nitrite levels have stayed at zero for a couple of weeks before getting more fish, and then a few at a time. It is generally safe to add in one go one third of the body mass of the fish already in the tank. You could get a shoal of one of the smaller loaches or even corydoras for the bottom. Note I said a shoal! These fish like company of their own kind. What do you have on the bottom of the tank? Loaches and cories need smooth gravel, or better still, sand. With mollies being big fish, you need to get tetras that are big enough not to be eaten. There is a slight chance that guppies and mollies can interbreed, though the offspring are usually weak and don't live long. Mollies need hard alkaline water but a lot of tetras need soft acid water - check on the fish database before buying.

One feature on the old Thinkfish was the Community Creator. You entered the  details of your tank, added fish and it would tell you of any problems like incompatible fish, not enough of a particular species etc. The CC was lost when the site had to change hosts, but the owner, Peter, is rebuilding a new improved CC. Once that is up and running, it will help you decide what fish you can add. Unless your filter bacteria multiply very quickly, it will be a few weeks before you can add your final fish.


One final comment - you say your nitrate was sky high. This could be for several reasons. A dead fish, as you suggest; too many fish; feeding too much; insufficient water changes.
20 to 30% a week sounds about right for a nicely stocked tank. It doesn't sound as if it was overstocked (except for the clown loaches) though bristlenoses like all plecs, do create a fair amount of waste. That leaves overfeeding and dead fish as a cause for the high nitrate. I know it's impossible to calculate, but you should be feeding the amount of food equal to one eye per fish. A fish's eye is about the same size as its stomach.
Once the tank is fully stocked again, keep an eye on the nitrate level. The highest it should be allowed to get is the amount in your tapwater plus 20 just before a weekly water change. If the reading is more than 20 above the tapwater level, you either have too many fish, are feeding too much, or not doing a big enough water change.




One last thought - did you check the pH when the fish died? It is possible for a tank to suffer a pH crash, and this sudden massive drop in pH can kill a lot of fish.

Unless you overstock, your water change regime of 20 to 30% a week is fine. While you are restocking, unless you see ammonia and/or nitrite, you'll be OK with that regime. But if you do see any ammonia/nitrite, you'll need to do water changes as necessary to keep them below 0.25.

With most loaches the absolute minimum is three, with more being better. But as most loaches (zebras includued) get quite big, it is a balancing act between having enough to keep them happy and not so many that you can't have anything else. I have dwarf chain loaches in my 125 litre, they are the smallest loach but are rather pricey.

Missing a day when feeding is perfectly fine. Lots of people do it. Also you could try feeding veggies once a week instead of their normal food. I find all my fish go mad for peas (cooked, deskinned and mashed). Have you tried your bristlenoses with courgette? You may find your new mollies like it too.

Just thought I'd better check about the pH; it was a small chance but it's as well to cover everything 

Hi regan, you've found the new site I see