Neolamp. Boulengeri

Two groups of different shellies should be fine in a 20G, as long as you have plenty of shells for them to choose from and call home. I breed Neo.brichardi (not a shell dweller but prefer same conditions) and use a mix of shell grit and fine gravel. A good filter is also very helpul, because they dislike large water changes. I never change more than 1/4 of the water at a time. You could also throw in a few livebearers to make the tank more active (platies, swordtail etc) as they are top swimmers and like alkaline water. I raise my neo.brichardi fry on Sera cyclops and they really grow.

Putting 2 different types of shellies in a 20 gallon tank is asking for hybrids. Esp. if they are both neolamps. You would be better off getting more of one variety.
You could also get a shellie and a smaller julie such as transcriptus.

I'm thinking of keeping shellies myself in my 20 gallon tall. I have just changed my substrate to sand and ordered some shells to prepare for them. Kit, when you say they dislike large water changes, what leads you to believe this? I read the same thing about altolamprologous calvus, and I am doing 50% water changes every 8-10 days and mine seems fine. It seems a little stressed during the water change but is back to normal within a couple of hours.

It is perfectly safe to do 50% water changes with Lake Tangs if you do not wish them to breed. They will often refuse to breed when managed with regular water changes (thus the tendancy by breeders to keep single pairs thus almost eliminating the need to water change). On the other hand Lake Malawi cichlids respond very well with up to 85% water changes. I keep a single pair in a 15G with a Eheim HOB. I almost never do any water changes other than topping up evaporation. Following this practice my Neolamprologu brichardi's produce a new batch of fry almost every 4 weeks on the clock. Once the fry are large enough to take small flakes I transfer them out to keep the bioload down.
I found a book called "African Cichlids" by Dr Paul V Loiselle and it has been really helpful and specific to each species needs. My brichardi's never bred until I followed the information in his book.

Thanks for the info Kit, in particular the reference to Loiselle's book. What type of Malawi cichid do you keep in your 15 g tank?

I've kept Neolamp. brevis, multifasciatus, similis, caudopunctatus, Lamp. ocellatus, meleagris, speciosus, and Altolamp. compressiceps "sumbu dwarf" types of shell dwellers. I disagree with the reference that they would hybridize in general. The meleagris, ocellatus, and speciosus might, and the similis and multifasciatus might, but in general, I doubt it would be a problem.

I do weekly 30% water changes on all of my tanks, including my breeding tanks. My shellies spawned regularly, and I also disagree that there would be any good reason to allow their water parameters to deteriorate by neglecting your water changes indefinitely. Nitrates are the end product of keeping our fish in little glass boxes. If you feed your fish, they build up, and must be removed with either water changes or live plants. Water changes also remove other dissolved organics, and enable you to keep your water parameters stable.

On a side note, I found that most shellies can effectively predate fry from other pairs in the same tank with them. My sumbu compressiceps can manage to protect their fry in a 40 gallon long, that's heavily planted, with one pair at each end of the tank. Other than that, I was only able to raise full batches of fry by placing a pair per tank. Then again, I wanted as many fry per spawn as possible. If that's not a priority, you will have a few of them live each time in a colony setting. The only exception to that, was my neo. multis, who spawned themselves out of house and home in a 30 gallon long, if I didn't continually thin them out.

Hope that helps

Barbie

I wasn't actually trying to encourage Lake Tang keepers to let water parameters deteriorate. I still test nitrates and nitrites regularly, I just reduce the water change volume and frequency with my Neo. brichardi's (usually 25% max) as opposed to my large SA/CA tanks. I found the frequency of breeding to be more regular when the tank is not as often disturbed by water changing, which can be achieved with a small bioload (and hence ability to maintain safe parameters). This coincides with Dr Loiselle's book. Today I moved out the larger fry to a growout tank, and did a water change. I expect now that the pair won't breed again for while as they readjust after the disturbance.

I wouldn't mix two types of shellies. Just my opinion. Especially if you cannot replace them. It only takes one of the little guys to snap and then you have some dead opponents. Shellies have attitude...alot is just that attitude, but they can and will get ready to rumble. If you had ocellatus I would definitely say "no". I haven't had the Boulis, so I am just basing it off my experience.